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Initials used as an abbreviation for the American Society for Testing and Materials. An organization devoted to the establishment of standard methods and procedures of testing materials. Copies of the approved test methods for urethane foam may be secured by supplying the identifying code number of the test plus the fee.


Normally used in the chemical sense of being a substance used to increase the rate of a chemical reaction, often used synonymously with the term catalyst, amine catalyst, or tin catalyst.


In normal foam industry practice, it is required that the chemicals used be weighed, pumped and dispensed within plus or minus 0.5% of the correct amount. Capability of operation within these narrow limits is available from most machine suppliers. See also 'metering accuracy' and 'shot accuracy';.

Acid Number

The value given to trace residues of acids in the finished polyol. It is of interest because acids can react directly with NCO groups (TDI) and thus must be allowed for in formulation calculations (see index). The normal value for most polyether polyols is less than .05 parts per hundred. Most polyester polyols normally have an acid number between 0.1 and 0.5.



Small mechanical parts that assist the joining of 2 dissimilar pieces, normally used to join pipes of different sizes or to assist in joining pipe to hose threads. Pipe threads are normally tapered while hose threads are straight.


A general term used to describe anything that may be added to the foam chemical mixture, not required in order to produce foam. It generally covers chemical classes such as plasticizers, colorants, reodorants, anti oxidants, fillers.

Adhesive Lamination

See lamination.

Adjustable Crossbar Height

A term used by liquid spreading device (reciprocator, traverser, spreader) manufacturers to describe the ability of machines to vary the height of the mixer discharge nozzle above the conveyor (or mold) by raising or lowering the crossbar or rails on which the mixer is riding. The adjustability may range from manually loosening bolts and lifting the crossbar into position up to automatic push button operation. Hand powered cranks turning built-in lifting screws are used for an intermediate type.

Adjustable Speed

A term used by machinery manufacturers to describe the ability of their pumps and mixers to be driven at different rates of speed. The minimum type covered by this somewhat all-inclusive term is a set screw adjusted split sheave (pulley). Other types range in complexity from manually rotated cranks or hand wheels up to automatic push button adjustment. Not all adjustable speeds are positive; thus some are not able to hold a setting after adjustment and others are not able to reset at the same markings in order to repeat the desired speed of rotation.

Adjustable Throughput


(See pre-cure and post-cure) a term used to refer to the period of time after all accelerated curing attempts have ceased during which maximum final physical properties are attained. Temperatures are usually maintained at 70-75° F during this period. Example: a molded flexible cushion may be pre-cured for 10 minutes at 250° F to develop enough properties to permit removal from the mold, then post-cured for 1/2 to 3 hours to reach 85% to 95% of the final properties, and then packaged and shipped during which time 'after-cure' continues until 100% of the properties are achieved. After-cure generally is not longer than 3 to 6 days with most formulations.


A term which describes material dripped from the discharge orifice of a self-cleaning mixing head after the continuous flow of liquid has ceased. It is usually objectionable and is influenced by mixer design, mixer wear, mixer cleanliness, material viscosity and flow characteristics, and leakage from the liquid delivery passages (metering ports). agitators-a term which usually refers to the mechanisms that mix and recirculate the various liquids within their tanks. These may be propellers, paddles, turbines, etc. Occasionally the term is used to describe the rotor or impeller that mixes the liquids together in the final mixing chamber, just prior to foaming.

Air Bleed

A term which refers to the practice of injecting very small amounts of compressed air (or other gas) into the mixing chamber or into the polyol stream prior to the mixing chamber in order to decrease the average cell diameter in the foam. A high degree of control over cell diameter can be achieved with a precision regulated air bleed system. See also 'catalyst air bleed adapter.'

Air Metering Device

A term which refers usually to a precision air bleed regulating system. Generally it includes regulators, filters, flowmeters, needle valves, check valves and also inline mixers.

Airless Spray

Method of atomizing a liquid stream for spray application purposes without using compressed air at the spray nozzle. Overspray and surface rebound are minimized.


(See also Aromatic) one of the main divisions of organic compounds (those containing carbon) and particularly indicates those compounds having ab open chain molecular structure.


An ambiguous term usually coupled with temperature and refers to the normal temperature of the particular room or environment in which the foam producing equipment or process is installed. It is often used to indicate U.S.A. house or factory temperatures of approximately 70° F.


A term which refers to a class of catalyst compounds used in the urethane foam reaction, These are characterized by having N or NH groups in the molecule and generally accelerate the 'blowing reaction' in preference to the 'gelling reaction'. The amines used as foam catalysts usually (but not necessarily) have a distinctive odor, and are miscible with water.

Amine Catalyst

See amine.

Amine Equivalent

An analysis value determined for isocyanate materials to express their reactive strength, used in some methods for calculating 'stoichiometric balance' of a formula . The value secured has an inverse relationship to the strength of the chemical as the larger the value, the weaker is the reactive strength of the isocyanate per unit of weight. For example, the amine equivalent value for pure TDI is approximately 87 while that of the less reactive crude 'polymeric isocyanates' may be over 130. The method of analysis may be obtained by request to one of the major chemical companies supplying the isocyanate.

Angle of Foam Rise

A term which refers to the angle formed between the rising foam front and the moving surface from which it is rising on a continuous slab process. This is usually critical for a given formula with an excessively large angle tending to cause cracking of the foam block, while too low an angle tends to cause excessive settling and splits. Adjustments to conveyor speed, chemical flow rate or conveyor angle are usually helpful. Under extreme conditions, the catalyst balance’ of the formulation or the processing temperature may have to be modified.


Is used to describe foam having different properties when tested along axes in different directions, e. g. parallel to foam rise as opposed to perpendicular to the foam rise. This difference occurs under conditions causing the individual bubbles to elongate in the direction of foam rise, creating a strong columnar structure parallel to foam rise and a weaker cylindrical structure perpendicular to the foam rise.


Materials which when added to a foam formulation improve the resistance of the foam to oxidative type reactions. Some of these materials retard the yellowing of flexible foam; some improve the aging characteristics of the final foam product under both dry and humid high heat conditions.

Antistatic Agents

Chemicals which impart a slight to moderate degree of electrical conductivity to plastic compounds, thus preventing the accumulation of electrostatic charges on finished articles. They may be incorporated in the materials before molding or applied to their surfaces after molding. They function either by being inherently conductive or by absorbing moisture from the air. Examples of antistatic additives are long-chain aliphatic amines and amides, phosphate esters, quaternary ammonium salts, polyethylene glycols, polyethylene glycol esters, and ethoxylated long-chain aliphatic amines.


A term sometimes used as a noun in describing the practical use of a particular formulation or piece of equipment. The use of urethane foam is often described in a manner such as 'an insulating application' or a 'spray-in-place application'.


A term used to describe an individual or company specializing in the application of foam to a surface or structure. It is often used to describe those who apply foam by spraying and thus are called 'spray applicators'.


A term which refers to a class of organic chemical compounds characterized by having a benzene ring type molecular structure. Tolylene diisocyanate is an example of this type chemical but other isocyanates may or may not be. See also aliphatic.

Artificial Ageing

The accelerated testing of plastics to determine their changes in properties such as dimensional stability, water resistance, resistance to chemical and solvents, light stability, and fatigue resistance.

Automatic Pressure Cut-Off

A term used to describe a control system on a metering unit in which a pressure surge or over-pressurization in the fluid circuit is sensed, actuating a relay which turns off the pump drive motor. This is an excellent safety-feature and does not affect the positive metering value of the system.

Automatic Solvent Flush

A term used to describe a solvent cleaning system for a urethane foam mixing and dispensing head. The usual system is activated by a push button which begins a cycle consisting of a timed amount of solvent, dispensed by a pressure pot or pump, injected into the solvent flush hose and then followed by a timed dispensing of compressed air blowing the solvent from the hose line into the mixing chamber and from there to the waste container. Both solvent and air timers can usually be adjusted to obtain optimum cleaning with maximum economy. A newer system termed 'fully automatic solvent flush' includes an additional timer which initiates the solvent cycle automatically if pouring has not occurred during a preset time period.

Auxiliary Blowing Agent

A term which usually describes a 'low temperature boiling solvent' type blowing agent added to a formulation deriving at least 80% of the gas required for foam expansion from the water-TDI reaction.

Back Cushion

A chair cushion that forms the back of the unit and is characterized by being leaned on rather than sat on. Generally a lower density, softer foam is used for a Back Cushion than is used for a 'seat cushion'.

Back Pressure

The higher upstream pressure developed by a restrictive valve or regulator.

Ball Rebound Test

One of several test methods for comparing various flexible foam samples for resilience (see Resilience Value). A steel ball of specified mass is dropped from a fixed height onto a foam sample, and the height of the rebound of the ball is recorded. The rebound height is divided by the original height to give a percentage. The method is a relative test rather than absolute, since the density of the foam has a strong influence on the results. The Test Method is described in ASTM D 1564-63T.

Barrier Coat

A term used to describe a clear or pigmented coating sprayed into a mold prior to foaming, which adheres to the foam and provides a base for further finishing steps. Usually used for rigid foam moldings finished to resemble wood.

Batch Mixer

A term which describes a type of mixer in which the entire amount of the formula required is poured or pumped into the mixing head and mixed for a definite period of time with multiple recirculation of the material through the mixing zone. The entire amount of the material is poured out of the mixing head at the conclusion of the mixing time period.

Batch Mixing

The process of simultaneously mixing the entire amount of the formula required in one container.

Batch Tank

A term normally used to describe the polyol or other premix tanks used in the flexible foam slab process. In this process some of the ingredients required are premixed in a Batch Tank in order to cut down on the number of components required to be metered into the final mixer or to eliminate the problems involved with metering very tiny amounts of materials into a continuously mixed stream. Also called 'machine tanks' to differentiate them from 'in-plant storage tanks'.

Belt Conveyor

A type of conveyor in which the conveying is performed by means of the movement of the top surface of the structure as a continuous ribbon or belt. The belt surfaces normally used in the urethane foam industry are metal, cloth or rubber. The commonest construction used in the flexible foam slab process is probably that of the interlocked metal belt.

Blanket Heater

A term which refers to the type heating device that is wrapped around a chemical tank to provide heat by conduction through the tank walls. Some of these heaters are equipped with variable thermostats; some are not. They are often used to supplement the in-line heaters when the chemical to be pumped has a high viscosity, creating a cavitation problem if not warmed.


A term used to describe a cut-off segment of the continuously produced loaf of flexible or rigid foam being made by the slab' technique. In some cases this Block would have top, bottom, and side skins intact and have cut surfaces only on the ends. In other cases the top, bottom and side skins may be removed by in-line trimmers leaving a smooth rectangular Block.

Blowing Agent

The chemical ingredient in the formulation that provides the gas creating the expansion of the foam. This can be either a low boiling chemical that vaporizes from the heat of the reaction such as fluorocarbon 11 or a chemical such as water that reacts with the isocyanate material to produce carbon dioxide. The low boiling chemical type formulation is usually referred to as 'solvent blown foam', while the other type is commonly referred to as 'water blown foam'. blowing reaction-one of the several chemical reactions occurring in the final mixture while it is foaming. It is most often used to refer to the chemical reaction resulting in the release of carbon dioxide.

Blown Elastomer

See elastomer.


Cavities that occur in the interior of the continuous foam slab as it is produced. Some of these cavities reach all the way to the top surface of the Block and can be seen ejecting little clouds of vapor just past the peak rise point. See flaps.

Board Foot

A standard of measurement in the foam and construction industry which refers to a square foot of material one inch in thickness. See super foot.


A descriptive term applied to foam that feels stiff and not flexible and yet is still in the flexible category. A typical foam of this type would require a small amount of force to cause an initial deflection in the foam and very little more force to deflect it to 50% or more of its thickness, and then a straight line increase in force is required for further deflection. See IFD (65/25) Index and plateau.

Board Stock

Sometimes used to describe the flat sheets of rigid or flexible foam cut from Blocks of foam. However, recently the term has been specifically applied to the product of a Continuous Lamination Foaming Line on which the foam is sandwiched between two skins.


Is a phenomenon that occurs when the gas being generated is not trapped in the liquid resin to make foam. It occurs usually if the surface active agents have been omitted or are defective, or if gelation is not occurring rapidly enough in relation to the speed of the blowing reaction.


A specially shaped Back Cushion, usually for Danish modern style couches or divans. The normal shape is a truncated wedge, although round, rectangular, and triangular are also available. The term is also used to describe a cylindrical, stiff pillow used for decorative purposes on a bed.


A synonym for gluing, adhering, laminating or rebonding. See rebonding.


A slang term referring to the pattern of high density streaks or flow lines that occur on the bottom of a foam Block when undercutting of the rising foam front occurs, or when shearing movements occur in the rising foam mass.


A mechanical device for drilling a long straight hole through a Block of foam in order to insert the mandrel used in 'log peeling''.


A term used in slightly different ways by many people but ordinarily refers to the presence of a scattering of cells 2 to 4 times larger than the uniform background cell diameter. If a thin section of the foam were cut from the Block, it would look as if a shotgun had blasted it with buckshot.

Buffered Catalyst

A catalyst, usually a very alkaline Amine, that has been partially or wholly neutralized with acid so that the reaction would not be affected by the extreme alkalinity of the catalyst. The general effect of the buffering is to slow the rate of the polymerization reaction.


Chemicals added to the formula that decrease the sensitivity of the formula to slight changes in the alkalinity or acidity of any of the components . They are also known as buffering agents.

Bulking Agent

A material or chemical added to another chemical that increases the quantity of the mixture required without changing the chemical reactivity of the total. The term is not only used to describe solid or powdered Additives, but is also used to refer to liquid Additives. An example is the bulking or dilution of the tin catalyst that is often used to gain greater control over the metering of very small quantities. In this case the tin catalyst is often diluted or bulked-up with a portion of the polyol. Barium sulfate is a solid bulking agent often added to the polyol to increase the density of the final foam product.

Bulk Storage

A series of tanks large enough in capacity that bulk shipments of one or more of the ingredients used in the formulation can be unloaded and stored directly on the premises. Also called 'in plant storage'.


Another synonym for Block.


A term used to describe what happens when a puff of gas is released during the formation of blows.


The common abbreviation for the cubic centimeter of the metric system. For liquid measurement the abbreviation ml (milliliter is often used in place of cc. The two measurements are approximately equal.)

CD Curve

A common abbreviation for Compression-Deflection curve.


An abbreviation for cubic feet per minute.


The abbreviation for centipoise.


The abbreviation for cycles per second. A recent international decision suggests the use of HERZ instead of CPS with reference to electrical wave motions. CPS is satisfactory for mechanical cycles.


The chemical symbol for carbon dioxide.

CO2 Blown Foam

Foam in which all of the gas for expanding or blowing is carbon dioxide, generated by the chemical reaction between water and the isocyanate material. This type foam is called 'water blown foam'.


A synonym for metering, referring to the weighing of carefully timed amounts of chemicals from the dispensing ports of the mixing head in order to set an exact ratio of flow rates between each component or to set an exact total


A term used to describe the filling of small molds with liquid, nonfoaming formulations of urethanes or other types of polymers, sometimes called solid elastomers or casting resins. Occasionally used to describe the potting of electrical or mechanical parts in foam.

Castor Oil Based Foam

Foam made from a formula in which the major polyol ingredient is derived from castor oil.


Technically, a chemical that has the property of being able to change the speed of a chemical reaction without apparently taking part in the reaction. Most of the so-called catalysts of urethane form reactions do have some part in the reaction and consequently do not fall under the proper definition, although they are often referred to by that name. (See Accelerator.)

Catalyst Air Bleed Adapter

A device used to surround a catalyst metering tube with a compressed air flow in order to prevent unwanted accumulation of foam around the port that could interfere with the flow of the liquid.

Catalyst Balance

The ratio between the Amine catalyst and the organotin catalyst. See reaction balance.

Catalyst Mix

A shortened form for catalyst mixture. Most formulations require delicate balancing between the blowing and gelation reactions, and consequently blends of different types of catalysts are often used together with an inert carrier or diluent to aid in metering accuracy or in miscibility.

Catalyst Solution

A synonym for catalyst mix.


Is synonymous with bubble or pore. It refers to the cavities left in the foam structure after the bubble walls have completely polymerized and solidified or curled back and fused into the boundary joints to form a skeletal structure. Cells can be closed (intact walls) or open (skeletal ribs only). Cell shape is more like an irregular polygon than a globe.

Cell Count

The number of cells or bubbles per linear inch or per centimeter. Cell count is very important to the physical properties of foam. See cell size.

Cell Membrane

The thin intact film that forms the bubble walls in closed cells, also called windows.

Cell Size

A term which refers to the average diameter of the pores (bubbles) in the filial foam product. Although often still referred to as fine, medium or coarse, or by the diameter in microns, most workers refer to the number of cells per linear inch (cell count).

Cell Structure

(See cell size) A term often used to point out overall uniformity of foam cell diameter. Example, 'uniform cell structure' describes foam with generally equal cell diameters.

Cellular Plastic (Expanded Plastic, Foamed Plastic)

A plastic with numerous cells disposed throughout its mass. The terms cellular, expanded, and foamed plastic are used synonymously. A cellular plastic may be produced by (1) incorporating a blowing agent which decomposes to liberate a gas; (2) mechanically stirring in a fluid or gas; (3) adding a water soluble salt or a solvent extractible agent to the mix prior to foaming then leaching out the agent after foaming to leave voids; or (4) other techniques.


1/100th of a poise, commonly used in describing the viscosities of the various chemical components in urethane foam. Although many formula viscosities are less than 2000 centipoise, some individual components may have viscosities as high as 100,000 to 200,000 centipoise. See poise.

Chain Extension

Is the lengthening of the spine or main chain of polymer molecules by end to end attachment usually involving condensation of functional groups between two or more molecules during the chemical (polymerization) reaction. Cross linking, a side to side attachment of molecules, also occurs during polymerization. Some physical properties are enhanced more by chain extension, others by cross linking.


A small scale or narrow undercutting of the expanding or rising foam front by a stream of the mixed clear liquid. This is usually due to wrinkles in the paper or uneven distribution of the liquid. Channeling often results in high density ridges on the bottom of the foam Block referred to by some as bones and others as striations or flow lines. Occasionally the term is used to refer to the condition arising when a heated portion of a viscous liquid is recirculated back into a tank without agitation, flowing immediately to the inlet of the pump without mixing with the cooler liquid.


A term occasionally used to describe the process of filling the machine tanks with the various quantities of chemicals.

Chemical Seals

The disks and flanges used to separate the foam ingredients from the operating mechanism, usually of a pressure gauge. The interior of the bourdon tube or bellows is filled, under vacuum conditions, with an inert fluid, up to the back side of the metal disk or diaphragm. This combination of liquid and membrane effectively isolates the mechanism without affecting Accuracy.


A heat exchanger used for cooling the chemical materials. Scraped surface, tube and shell, and plate type exchangers are all used, with the scraped surface being the most efficient, particularly with the higher viscosity materials,

Chiller Package

A heat exchanger used for cooling the material but including the cooling source. It usually consists of a scraped surface, tube and shell, or plate type heat exchanger plus a refrigeration compressor and controls. The package unit may be a direct expansion type in which the refrigerant expands directly into the main heat exchanger or it may be of the liquid transfer type in which the refrigerant gas expands into an intermediate heat exchanger, and then a circulating liquid is used to conduct the heat from the main heat exchanger. See cooling media.


A term sometimes used to describe the in-line type cut-off saw, and sometimes used to describe a device used to cut or chop urethane foam trims into small pieces for rebonding, stuffing toys, pillows, etc. See crumb.

Clean-Out Type Chemical Seal

A special type chemical seal permitting cleaning of the chemicals side of the disk without complete disassembly. See chemical seal.

Clickable Foam

Foam that recovers 100% from the pinching effects of clicking.


The process of stamping out irregular shaped articles from thin sheets of foam by means of a hammering mechanism and a steel-rule die. See die cutting.

Closed Cells

Is the property of a foam of having each individual bubble completely sealed off from its neighbor so that no exchange of gas can take place except by diffusion through the walls, With rigid foams, it is usual to try for 100% closed cells to achieve maximum thermal insulating ability and minimum water pickup. With flexible foams, it is normal to try for 100% open cells for maximum flexibility, resilience, and breathability even to the extent of achieving a true skeletal foam in which even the broken membranes between cells have been removed or fused back into the ribs."

Closed Molding

The practice of molding a foam object in a cavity in which the foaming liquid is 100% contained with only gas being allowed to escape.

Coarse Cells

Very large bubbles averaging not over 20 to 30 cells per lineal inch. See cell size.

Cold Molding

The process of flexible foam molding in which the molds are maintained at temperatures between approximately 100° F and 150° F as compared with the alternate "one shot" molding technique in which temperatures of 250° F to 350° F are obtained within one minute of pouring. Flexible prepolymer molding normally has utilized temperatures in the "cold molding" range.


The sudden or complete loss of height occurring after the foam has partially or completely expanded. Under extreme conditions, the foaming chemical mixture may not expand at all but may merely boil violently and then harden into a solid sheet. See boiling.


A dye or pigment used to color the foam for appearance, identification, or for other sales purposes. Occasionally a necessary minor ingredient may act as a colorant.

Complete Package

A term normally used by those interested in continuous slab processing and referring to all of the equipment required to make a product. This comprehensive list generally includes the paper handling equipment, chemical handling equipment, the foam machine, the conveyors, the spreading or traversing device, curing devices or ovens, cutting equipment and packaging equipment. Testing equipment and technical service may or may not be included.


A term used to describe a separately metered stream of liquid that will be directly introduced into the mixing head for the final mixing. Although as many as 11 or more chemical components may be used in a formulation, these may be preblended into as few as two components for the final formulation used in the machine. See number of components.

Compression Load Deflection (CLD)

The determination of the resistance to compression of a foam sample when the entire area of the sample is compressed. This Test Method is described in ASTM.

Compression Set

An industry expression used to describe the recovery of foam from static or fixed compression. Less than 10% compression set (which is greater than 90% recovery) is usually accepted as good. Also called 'percent set.' This Test Method is described in ASTM D 1564-63T.

Compressive Strength

A term primarily used to describe the resistance of rigid foam to compression. This test method is described in ASTM D 1621-59T.

Continuous Mixing Head (Continuous Mixer)

A mixing device capable of dispensing homogeneously mixed material continuously, without affecting the temperature or pressure of the mixture by virtue of its continuous operation. The individual components may be valved as in the 'on-off' mixing heads, but are not required to be. Instantaneous start and/or stop of all components is not essential, although desirable.

Continuous Slab

The production of a continuous, homogeneous, seamless loaf of urethane or other foam by laying down a uniformly distributed liquid film of mixed materials on a conveyor belt moving beneath the mixing head at such a rate of speed as to form a stable rising front of foam. The process may only last for a few minutes, or it may run for 24 hours per day depending on sales requirements.

Conventional System

A method of foam production in which the mixed material being discharged from the mixing head is a clear liquid. This term is used to differentiate between non- frothed (conventional) and frothed systems of production.


A term which refers to the process of cutting and shaping used to convert bread loaf shaped slab foam Blocks into saleable items.

Conveyor Belt

An endless loop of material, either metal, cloth, rubber, or paper, used to carry the expanding foam mixture in the manufacture of continuous slab foam. The types are usually further described as 'linked metal', 'slat type metal', 'rubber' (even when fabric reinforced), 'cloth', 'cotton', or 'canvas belt'.

Convoluting Cutting

The splitting of a sheet of flexible foam while it is variably compressed so that two matching pieces of foam are created, each with alternating patterns of hills and hollows on their adjacent sides. The main advantages are that the foam can be made softer and more resilient mechanically and that two pieces of foam are produced, each of which is almost as thick as the original piece.

Cooling Media

The material that carries the heat away from the chemicals. In the direct expansion type of heat exchanger, the refrigerant gas is the cooling medium; in the liquid transfer or 'brine' cooled type of heat exchanger, the ‘brine' is the cooling medium for the chemicals and the refrigerant gas is the cooling medium for the 'brine'. In most modern cases, a solution of ethylene glycol permanent anti-freeze is used for the 'brine' solution rather than the salt solution. See chiller package.

Core Density

The density of the foam at the center of the foam object. In most cases, foam will form a density gradient in an object with the highest density being at the outer or skin surfaces and the lowest density being in the center or core of the object.


Long narrow openings or cavities in the foam Block that have widely separated and relatively smooth sides. These are subdivided into side cracks, top cracks and pocket blows (internal cracks) for trouble shooting purposes. See the specific headings for more detailed descriptions.

Cratering (Moon Cratering)

The condition in which the top surface of the continuous slab of foam resembles a photograph of the surface of the moon. It is normally caused by entrapment of very large gas bubbles that may have originated in the mixer or developed from excessive lay down splashing or possibly liquid undercutting (channeling) the foam front.

Crazy Balls

Globules which may pop to the surface of the foam front under certain conditions of flexible slab foam manufacture. The balls may race madly down the slope of the rising foam front or dash erratically around on the surface or just beneath the surface of the rising foam.

Cream Line

The point on a continuous foam slab conveyor where the clear mixed liquid becomes cloudy and begins to expand. When streamers are present, they extend upstream from the cream line into the clear material. When all variables have been stabilized during a production run, the cream line will remain at a fixed distance downstream from the mixing head.

Cream Time

A time interval defined somewhat differently between a laboratory batch or hand mix and a production machine mixer. The laboratory or batch type mixing definition is usually 'the time between the start of the final mixing and the point at which the clear mixture turns creamy or cloudy and starts to expand'. With the machine mixing process the cream time is generally taken to be 'the time between the first material being poured until that material turns creamy or cloudy'. Occasional misunderstandings arise over this and over the occasional practice of labeling the time between final mixing and the start of creaming or foaming as 'cream time' for laboratory or Batch Mixing when it could more properly he termed 'liquid handling time'. The problem results from the fact that laboratory type mixing requires as much as 100 times more mixing time than machine mixing. "Frothing" masks the cream time but usually extends the overall 'handling time'.


The dimensional change with time of a material under load, following the initial instantaneous elastic deformation, Creep at room temperature is sometimes called Cold Flow.

Cross Linking

Applied to polymer molecules, the setting-up of chemical links between the molecular chains. When extensive, as in most thermosetting resins, cross-linking makes one infusible super-molecule of all the chains.


A term used by the furniture industry to describe a mattress or cushion that is thicker in the middle than it is at any edge. This is much easier to achieve with molded articles but can be achieved for slab produced articles with the use of special cutting or abrading machines.

Crude Isocyanate

Is a term sometimes used to describe an undistilled isocyanate mixture containing several different polymeric isocyanates. These mixtures are ordinarily a dark brown in color as opposed to the clear water white color of distilled TDP. Some chemical manufactures object to the description 'crude' and consequently many prefer the term 'polymeric' isocyanate or 'undistilled' isocyanate.


A term used to describe very finely divided pieces of flexible urethane foam that have been shredded, ground, milled or torn from flexible foam trims or scraps.

Cubic Centimeter

A common metric measure of volume developed from lineal measurement. There are approximately 16.4 cubic centimeters in a cubic inch. The liter is a preferred volumetric measurement, particularly liquids. One milliliter (ml) is approximately equal to 1cc.

Cubic Foot

A common measure of volume in the English System. This is a cube with length, width and height all equal to 1 foot. There are 1,728 cubic inches in a cubic foot. See cubic centimeter.

Cubic Meter

A common measure of volume in the metric system developed from lineal measurement. This is a cube with length, width, and height all equal to 1 meter. Since there are 100 centimeters in a meter, there would be 1 million cc’s in a cubic meter. There are approximately 35.3 cubic feet in a cubic meter. A meter is approximately 39.4 inches in length.


A term which refers to the completeness of the chemical reaction. At 100% completion, the foam should have 100% of the maximum physical properties attainable with that particular formulation used. Because 100% cure is not always reached in a practical length of time, some arbitrary time- temperature period is usually assigned to a particular formula to designate a practical level of cure at which testing for physical properties may be started. See cure time.

Cure Oven

The final oven into which foam articles are placed in order to achieve the desired final level of accelerated cure. The term is sometimes ambiguous in normal use and is usually qualified with a prefix or another word to make it more specific, such as pre-cure or post-cure.

Cure Time

The time required to achieve a specified level of cure. See pre-cure, post-cure and handling time.

Curtain Wall Panel

Any type of panel that is hung on the outside of a building to form the exterior skin of the building, without bearing any structural load other than that which itself generates, sandwich panels with a foam core are often used in this type application.

Cut-Off Saw

A special type of foam cutting saw that is used to make vertical cuts. The traveling cut-off saw is used to make cuts on a continuous slab line in a direction across or perpendicular to the direction of foam movement, while the foam is moving. The stationary cut-off saw is used to cut long slabs into shorter slabs while the foam slab is stationary. This type of cutter is normally a special band saw, having the blades twisted 90" from the plane of the wheel surfaces in order to avoid interference problems with the saw wheels or the other portion of the blade. Another version of this type saw is based on the vibrating bayonet type of blade.


Is a registered trademark used for triethylenediamine, a very powerful Accelerator or catalyst of the tertiary Amine family. It is used as a highly selective blowing reaction catalyst for flexible foam and a more general catalyst for rigid foams.


Day Tanks

A slang expression generally meaning either Batch Tanks or machine tanks used for one day’s production run. The tanks may not have to be very large as a 'daily' production run may be only 20 minutes long for some factories.

Decorator Pillows

Small, variously shaped pillows, usually with bright colors, that are thrown onto chairs and sofas for color accent or general decoration. Also called throw pillows or occasional pillows.

Degree of Polymerization (DP)

The number of structural units or mers in the 'average' polymer molecule in a particular sample. In most plastics the DP must reach several thousand if worthwhile physical properties are to be had.

Demolding Time

The time between pouring the liquid into the mold and the removal of the foamed article from the mold. This is usually kept to the minimum possible time in which the partially cured object can be handled without damage, since it is more economical to reuse the molds as quickly as possible.


The weight of a specified volume of material (foam). In some countries this is expressed as pounds per cubic foot; in others it is expressed as grams per cubic centimeter or kilograms per cubic meter.

Density Profile

The graph plotted from variations in density occurring in foam samples due to physical problems of heat loss, surface wetting, and shearing of foam during movement. Because of these factors, most foamed articles exhibit a variation in density from the outer skin into the geometrical center. When this variation is plotted on a graph, the result is a density profile shaped like the letter 'U'.

Dibutyltin Diacetate

Is a powerful catalyst of the organotin group. See organotin catalysts.

Dibutyltin Di-Ethyl Hexoate

Is a powerful catalyst of the organotin group. This is one of the best, but is, unfortunately, not destroyed by the heat of reaction. See organotin catalysts.

Dibutyltin Dilaurate

Is a powerful catalyst of the organotin group. It is sometimes used for rigid foam and for adhesives. See organotin catalysts.

Die Cutting

The process whereby shaped foam articles are stamped out of a sheet of foam by the impact of a die against the sheet of foam. This can be done by an impact device hitting a steel-rule type die on an individual basis, or by a special roller die compressing the foam sheet against a cutting bar or roller on a continuous basis. This is a low cost method of providing very unusual shapes. Another name for this process is 'clicking'. The lowest cost dies for this type work are called 'steel rule dies' and consist of specially shaped, sharp edged steel straps imbedded in a wooden backing. See also clicking and clickable foam.

Differential Thermal Analysis

Is an examination technique whereby the foam may be heated to destruction while a temperature profile recording is being taken. This test assists the developmental chemists and engineers to better understand the behavior of foams during exposure to high temperature and flames.


Is one of the major chemicals used in the manufacture of urethane foam, particularly flexible foam and rigid prepolymer intermediates. Tolylene diisocyanate (TDI), which is currently the most popular one, is an Aromatic chemical having a benzene ring type structure and two isocyanate (NCO) groups attached to two of the six possible positions. The most commonly used type of TDI is a mixture with approximately 80% of the molecules having one of the NCO groups in the ortho position and one in the para position with the other 20% of the molecules having both NCO groups in the ortho position. One of the reasons for the warning against allowing this type material to freeze is that these two isomers will selectively separate during freezing, changing final foam properties if reacted partly frozen.


Is a term sometimes applied to a liquid that resists being moved but is quite fluid at rest. Some of the polyols used in the manufacture of urethane foam are not Newtonian (water- like) fluids and can be described by this term. They are characterized as being very difficult to handle, particularly at higher flow rates. The phrase 'high elastic component of viscosity' is also used.


A material used to extend or bulk up another material without changing the reactivity of the original material other than by the dilution occurring. The term is usually applied to fluids; whereas the words bulking agent, extender and filler are generally used with solids. This type material is also called 'liquid filler'.

Dimensional Stability

Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.


A substance (comprising molecules) formed from two molecules of a monomer.


A polyol or resinous material having two reactive hydroxyl (OH) groups attached to each molecule.

Discharge Orifice

The port or opening through which the chemicals are discharged. This term is usually restricted to the final discharge of the mixed materials rather than to intermediate points opening into the mixing chamber, which are normally called metering ports or metering tubes'.


The gradual yellowing of urethane foam due to a photochemical reaction occurring from the effect of certain wave lengths of light. It is faster in sunlight than in artificial light, although it occurs in both. At the moment there is no inexpensive method of prevention, although several methods are in use to retard the reaction and to lessen the final extreme of discoloration. It is possible to mask the reaction through the use of colorants. Occasionally fresh foam will discolor in the center of the Block for several reasons, one of which may be an excessively high internal temperature.

Distribution Block

A term which on urethane foam equipment refers to a manifold arrangement used on continuous or non-recirculating systems for collecting the various component streams together to enter the mixing chamber. There is no valving in this type Block, although there may be valves in the feed lines.

Double Cells

A slang term used by some as a synonym for buckshotting.

Dribble Marks

Long lines of undesirable large bubbles rather close together and usually just under the top skin of Blocks of slab foam. They generally result from a combination of excessive channeling and too much air entrapped in the liquid deposited on the moving conveyor belt. The channeling tends to line up the bubbles and carry them under the foam front resulting in dribble marks. These unsightly chains of bubbles create a low tensile line at which tears or rips can easily initiate.

Dry Heat Aging

An accelerated aging test that helps to screen out formulations that may have a tendency to deteriorate too rapidly under certain climatic conditions. The foam samples are exposed to dry heat for varying periods of time as specified in ASTM Test Method D 1564-63T.

Dynamic Balance

A term sometimes used to describe the stability achieved after all operating variables are in balance on a continuous slab foam production line, and the cream line and peak rise point remain at an exact point indefinitely.

Either-Or (Combination) Mixing Head

A mixing head capable of being used for conventional or froth pours with no modifications other than the substitution of metering ports or 'mixer housings'.

Elastic Component of Viscosity

A term used to describe the resistance of some fluids to flowing under certain conditions of shear and applied force. Under these conditions the liquid may behave more like a rubber than a water-like fluid, See dilantic.

Elastic-Fluid Behavior

See elastic component of viscosity.

Elastic Limit

The point of deformation beyond which a material will permanently deform rather than elastically recover. See yield point. The Method of Test for this is described in ASTM E 6-61.

Elastic Modulus

A ratio between the force applied to cause the deformation and the resistance to that force by the material being deformed. It can be determined for samples in tension as well as compression. Where a straight line graph is not produced, a tangent line to the largest part of the curve is used to express the ratio. The modulus must be determined below the point at which the elastic limit is reached.


A rubber-like material not necessarily made from what we conventionally think of as rubber. In the urethane industry, elastomers are ordinarily thought of as the solid or non-foamed materials, but there are exceptions known as "blown elastomers" which have been foamed by methods conventionally used for expanding rubber rather than the methods used to make urethane foam.


The percent of its original length to which a specially shaped sample will stretch before breaking. The Test Method is described in ASTM D 1564-63T.


Are Additives to a formulation that aid in stabilizing a mixture, between the time it is mixed and poured and the time it starts to foam, by the formation of an emulsion. This becomes important at times as not all the isocyanate materials are readily miscible with all polyols or resins creating a tendency to separate quickly after the mixing of the components .


A suspension of fine droplets of one liquid in another.

Equivalent Weight

Is the molecular weight of a chemical divided by the number of reactive (functional) groups. For example, the molecular weight of pure TDI is 174, the number of reactive groups is two (it is a diisocyanate) so the equivalent weight is 174/2 or 87. In a formulation, the number of equivalents of TDI must be balanced against the number of equivalents of water and polyol in order to achieve stoichiometry. The equivalent weight of isocyanate materials is often determined by the Amine equivalent test method and consequently the equivalent weight of the material may be called the 'Amine equivalents'.


The heat liberated by some of the chemical reactions occurring in the foaming mass. Urethane foam reactions fall in the general class of exothermic reactions, which have heat as a by-product. Under some conditions this heat becomes excessive and can damage the foam. Large pours or high density formulations are particularly critical in this respect because of the excellent insulating ability of the foam.

External Mix

The final mixing of the liquid ingredients outside the final discharge nozzle on the way to the target surface. This is normally accomplished by turbulence created by air jets, and thus the mechanism or device is usually classed as a spray gun. An advantage of this type mixer is that a solvent flush is theoretically not required.

Eyeball In

A slang expression meaning to adjust as closely as possible to the desired instrument setting by visual means or by sense of touch or feel without making mechanical cross-checks.


An apparatus for determining the resistance of resins and other materials to fading. This apparatus accelerates the fading by subjecting the article to high intensity ultraviolet rays of approximately the same wave length as those found in sunlight.

False RMA

A term which refers to the practice of increasing the initial RMA of a foam sample by formulation techniques which give only a temporary boost in firmness that is soon lost in normal use (flexing) of the foam product. See flex fatigue.

Fast Heat

Intense heat supplied to a mold in order to raise the temperature of the mold-foam interface to 250° F. or higher within 1 or 2 minutes after the pour. This has been found to shorten the handling time, and to improve the quality of the skin and ha1 physical properties of the molded article. This is used in 'one shot' flexible foam molding.

Fast Heat Oven

An oven capable of supplying the intense heat required for the fast heat process. The most common type are those using either gas or electric radiant heat.


An inert material added to the foam formulation to change the final physical properties. Normally fillers are used to increase the density of the product without significantly adding to the cost, or they are used to assist in a cost reduction. The solid fillers often result in higher load bearing properties but lower tensile and tear strengths.


A device to remove unwanted particles of material from the liquid streams of chemicals. For trouble free operation all lines should be properly filtered.

Fine Cells

A term which is used to describe foam with a cell count of 80 or more per lineal inch, See cell size.


A foam industry term used to describe the reaction of foam to a point indentation such as would occur when pressing a fingernail firmly into the foam article. 'Good Fingernail' means rapid recovery with no permanent marking. 'Poor Fingernail' means slow recovery or failure to recover leaving a line or point impression in the foam. With experience this can be a useful screening test for relative comparisons between foams.

Fixed Calibration Time

The practice of metering the various fluid streams during a fixed time interval such as 6 seconds or 1 minute in order to calibrate and set the liquid streams to a desired total flow rate per minute as well as to a desired ratio with each other.

Fixed Ratio

The condition of having all components with a fixed throughput so that ratio variations are not possible. See Ratio Control.

Fixed Throughput (Fixed Flow rate)

A term used to describe a machine with one or more pumps directly connected to the drive motors so that no variation in flow rate is possible.


An ambiguous term used at times to describe the more permanently installed portions of the mechanical handling devices needed in order to load and unload molds and to carry them through the curing area. The term jigs is sometimes used to describe that portion of the total that aids in fastening the molds to the fixtures.


A slang term used to describe many small splits scattered widely throughout and on the top surface of a foam slab or Block. This is usually seen in flexible slab production when the gelation or polymerization reaction has been excessively retarded in relation to the blowing' reaction.

Flame Lamination

The practice of sticking together or gluing flexible foam and fabric by melting one surface of the foam with radiant heat and quickly pressing it to the fabric before the melted material resolidifies. For best results a slightly thermoplastic formulation of foam (normally classed as a thermoset) is needed. See definition of thermoset and thermoplastic.

Flame Retardent

Has several meanings according to the Test Method used. In general, it can be said that a flame retardent material imparts a certain degree of flame retardancy to a foam, i. e. the foam will burn less rapidly or lose less weight on burning.


Describes the relative burnability of the material in a specified situation. Meanings vary according to the test method used.


The external symptom of large internal blows or voids. These generally develop just past the peak rise point and are usually semi-circular tears in the top skin that connect with the internal voids. Under extreme conditions they may occur prior to the peak rise point.

Flashing or Sparkling

A condition in continuous slab foaming, during which there is a continual release of tiny bubbles of gas from the surface of the mixed material just after it has been poured on the conveyor. It may continue until the foam has partially expanded. Under certain conditions of light reflection, the foam appears to sparkle. It resembles boiling to some extent, but the bubbles are so tiny that no collapse occurs and foaming proceeds normally as soon as the material viscosity has increased to the point in which all gas is trapped.

Flat Blade Impeller

A mixing blade that is characterized by a generally single plane shape or flat appearance. It may be solid, perforated with various patterns, or may be irregular in contour.

Flex Fatigue

The loss of physical properties of a foam sample undergoing continuous flexing of a specified magnitude, duration and rate. The Test Method is described in ASTM D 1564-63T.

Flexible Mold Material

The rubber like material used for molding very intricate shapes and contours into rigid foam. These materials can be any elastomers but are more usually urethane or silicone based. The usual compounds are liquids which are poured over the 'master', allowed to gel, then removed and oven cured to maximum tensile strength before use.

Flexible Molds

Molds made of rubber or elastomeric plastics used for casting plastics. They can be stretched to remove cured pieces with undercuts.

Flexible Shaft Adapter

A special metal spindle that attaches to a motor shaft at one end and permits coupling of the flexible shaft to the other. These Adapters are different for each motor shaft size and for each flexible shaft size.

Flexible Shaft Mixer Drive

A long flexible coupling between the mixer drive motor and the mixing head. This type drive shaft is often used when the mixing head must be moved during operation. The drive motor is remotely located in order to cut down on the weight and inertia of the mixing head assembly. Durability of the shaft is good if properly installed and used according to the manufacturer’s specifications. This arrangement is also called 'remote drive'.

Flexible Strength

The strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure. With plastics, this value is usually higher than the straight tensile strength.

Floating Lid

A term used to describe a special lid used on some flexible foam cushion molds. The lid, which has a specified weight per square inch, is suspended above the foam at a position near the desired maximum rise and is free to float on the surface of the rising foam against the gradually increasing compression of springs. The use of this type lid appears to minimize the appearance of loose skin and hard spots in the cushions.


Rate of all chemicals.

Flow Lines

A term which refers to a pattern of high density streaks or ridges radiating upward from the bottom of a Block of flexible slab foam. They are usually caused by undercutting (channeling) of the foam front or pouring freshly mixed materials on top of rising foam. See bones.


A flow indicating device usually consisting of a glass tube containing a float which rises or falls in response to variations in flow of a fluid through the tube. These are usually not accurate enough to serve as anything other than 'guides' to metering.


A term which refers to the quantity of chemicals delivered to the discharge nozzle or metering port in a specified time interval, usually expressed in pounds per minute per component, in the USA. 'Total flow rate' would be the quantity of mixed liquid discharged from the mixing chamber in the required time interval (the total of all individual component flow rates).


A term which refers to the general family of fluorinated hydrocarbons to which belong some of the most popular low temperature boiling chemicals used as blowing agents.

Fluorocarbon Blown Foam

Foam produced entirely by the gas generated from the boiling of a fluorocarbon, such as trichlorofluoromethane (R-11).


In the sense the term is used in the urethane foam industry, a product, either flexible or rigid, that has been produced by the internal generation or liberation of a gas in a fluid medium that is simultaneously polymerizing while expanding in volume, The bubbles that make up the final product may be completely interconnected (open celled) or walled off from each other (closed cell).

Foam Fatigue

The loss of physical properties of a foam article in use. Some loss is to be expected. The most noticed problem is the softening of cushions. Better quality foams would ordinarily be expected to fatigue less than poor quality foams.


Refers to the deposition of foams and requires that the foaming machine be brought to the work which is 'in place' as opposed to bringing the work to the foaming machine.

Foam Line

See cream line (Also refers to a foam producing assembly line)


The list of ingredients and their proportions to each other which must be used to make a particular foam product.


A term used either as a synonym for formula (the list) or used to refer to the chemicals that would be used in the preparation of a foam from a formula.

Free Rise (Unrestrained)

The unhampered expansion of a foam sample or product in a container with no top and a height of side wall not greater than twice the diameter. This is normally used in most laboratory sample screening work and is the normal condition in the slab process. The lowest possible density with a particular formula is attained under free rise conditions.

Friable (Foam)

A term used to describe rigid foam with such a low tensile strength that any wiping of the surface or jarring of the sample produces a fine powdery dust. Some formulations go through a friable stage of cure, others remain friable permanently. This is generally regarded as a highly undesirable property.

Froth (Frothing, Froth Process)

A term which refers to the practice of incorporating an unusually low boiling material into the final foam mixture (in a pressurized mixing chamber). When this liquid is discharged from the pressurized chamber, it expands instantly into a semi-liquid foam (froth). In normal practice enough of the special frothing gas is added to the mix so that this initial or pre-expansion produces approximately one third of the total expansion of foam required. The remainder of the expansion is by the normal procedure. Fluorocarbon 12 is the most common low boiling liquid used for frothing.

Froth Mixing Head

A mixing device for urethane foam that is designed for introducing the low boiling point frothing agent into the mixing chamber as a liquid and is capable of withstanding internal pressurization up to approximately 250 psig. in the mixing chamber without leakage problems.

Froth Spray

The practice of atomizing a frothed discharge from a mixer and spraying the particles of semi-expanded material onto a vertical or overhead surface. This has the advantage of practically no slump on a surface, over widely varying temperatures, and results in minimum final foam density due to self insulation from the surface on which the froth spray is applied. The final product has the disadvantage at present of a rather irregular surface.

Full Recirculation

A term applied to a urethane foam machine designed to permit all fluid components to be circulated between the tank and the mixing head during the 'idle' or non-production time. For 'full recirculation' the valve that diverts the flow to the mixing chamber should be immediately adjacent to the chamber so that stagnant areas are eliminated. See short recycle valving.

Fully Automatic Solvent Flush

The solvent flush cycle is initiated automatically by the machine.


The number of reactive groups attached to a single molecule. A polyol with a functionality of 2 would be a diol.

Furniture Foam

Rigid urethane foam of a quality, density and appearance suitable for replacing wood products. Most of the formulations would produce foam in the 25 to 30 pound per cubic foot density range (similar to white pine) although lower density foams are available.

Gas Loss

The net weight loss of chemicals during foam production, determined by subtracting the total weight of foam produced from the total weight of chemicals used. In most cases this refers only to the carbon dioxide generated in a water blown formula . In some cases it is used to refer to evaporation and eventual loss of the fluorocarbon. To avoid confusion the type of gas loss should be specified.

Gel Coat

A thin coating of a high quality polyester plastic applied to the surface of a mold prior to filling the mold with foam. The foam adheres to the gel coat so that the part, when removed from the mold is finished.

Gel Strength

An expression of the stability of the foaming mass. This is at least partly dependent on the increasing viscosity of the liquid. A foam with high gel strength would be very stable and could withstand more shearing stresses in molding than could a formulation with low gel strength.

Gelation Rate

The speed with which the chain extension and cross linking reactions are occurring in the foaming mass. This rate of reaction must be balanced with the rate of gas generation so that gelation occurs just after peak foam rise in order to achieve the best quality product. See reaction balance.

Gelling Reaction

The increase in viscosity of the foaming mass caused by the polymerization of the liquid chemicals. See polymerization reaction.

General Purpose Foams

Foams or formulations that are capable of being used in a wide variety of Applications without modification while still attaining a reasonably high level of physical properties.


Is the generic terms for polyols having a functionality of 2, also termed diols.


A term used to refer to a machine used to produce small foam particles from foam trim. These devices are also called shredders, cutters and hammer mills. See crumb.

Guard Thermostat

An extra thermostat in the electrical circuit of a heating system, used as a safety control over the maximum temperature of the heating source.


The chemical symbol used to represent water.

H2O Blown Foam

Hand Batching

The practice of weighing all the ingredients of a foam formula separately into a mixing container and stirring the mixture with a spatula or paddle for the appropriate mixing period, then pouring this mixture into a mold. Although usually practiced only in laboratories, there are some commercial operations based on this method.

Handling Time

The time, in a molding process, between either the start or the completion of the pour and removal of the product from the mold without damage. In the continuous slab process it is often referred to as the time between deposition of the liquid mixture on the conveyor and the time the foamed Block containing the specified portion of chemicals can be lifted from the conveyor and handled without damage. In Batch Mixing it can also be 'the time between completion of mixing and pouring into the mold.' See cream time.

Hard Spots

A term which refers to the firm high density areas formed in a molded object when packing is excessive or poor distribution occurs. This firm area or hard spot is normally caused by a localized collapse, filled in again by excess foam from the surrounding area.


The smoke or fumes released from the foaming mass under normal conditions of continuous slab processing, particularly at peak rise or just after. Under exceptional atmospheric conditions, the smoke or haze may obscure the surface of a large area of the conveyor.


A shortened form of the word mixing head, used to describe devices ranging in complexity from simple manifolds to complex diverting valves having attached mixing chambers, impellers, drive motors, etc.

Head Mounted Drive

A mixing head drive motor that is mounted adjacent to the mixing head and is directly connected by framework to it. See flexible shaft mixer drive and remote drive.

Health Bubbles

Little bubbles popping up through the top skin of a continuous flexible slab or free rise flexible foam pour just past peak rise. From the very first days of the industry this was recognized as a sign that the resultant foam would be open celled and generally of good quality. The word is a direct translation from the German phrase brought to the USA with early technology. The bubbles do not have to be present to make good foam but their presence does no harm and is psychologically reassuring,

Heat Distortion Temperature

The temperature at which a sample of foam will begin to change dimensions under specified conditions of loading and environment. The Test Method is described in ASTM D 794-49, but the temperatures and times used are varied to suit the end use.

Heat Exchanger, Multiple Pass

A heat exchanger for either heating or cooling one of the chemical components that does not have sufficient capacity to bring that component to the desired temperature in a single journey or pass through, but rather requires multiple recirculations of the component to condition the material properly.

Heat Exchanger, Package

A heat exchanger combined into a single unit with its source of heating or cooling. An example would be a scraped surface heat exchanger with an attached refrigeration compressor that can be reverse cycled to provide both heating and cooling. heat exchanger, scraped surface-a heat exchanger so constructed that the heat conductive surface is continually scraped to remove the temperature conditioned material. This type is normally used for cooling those materials that tend to increase in viscosity enough to stick to chilled surfaces, interfering with the efficiency of the unit.

Heat Exchanger, Single Pass

A heat exchanger for either heating or cooling one of the chemical components that has sufficient capacity and control instrumentation to bring that component to the desired temperature in one journey or passage through.

Heat Exchanger, Tube and Shell (T & S)

A heat exchanger constructed of a bundle of tubes inside an outer casing or shell. This type is used for either heating or cooling of those components having low enough viscosity not to interfere seriously with the efficiency of the heat exchange surface. The chemicals to be conditioned may be circulated either through the tube or through the shell portion.

Heat Of Reaction

See exotherm.

Heating Media

The liquids or gases used to convey heat to or from a heat exchange surface. See cooling media.


A method of joining plastic films by simultaneous Application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically.

Heavy Skin

Is the condition in free rise or molded articles of having a very thick, high density, outer skin. This is generally undesirable economically in flexible slab foam and can be caused by a defect in the formulation or in the environment. It is highly desirable in some molded articles, both flexible and rigid. Self skinning or integral skin.

Helical Spiral Mixing

More properly termed 'stator helix mixing', a term used to describe the practice of mixing the chemicals by means of turbulent flow conditions created by injecting a high velocity gas stream into a helically spiraled pathway simultaneously with the individual chemicals. The developmental work on this type mixing was performed by the duPont Company in an effort to create a light weight low cost froth dispenser. The stator helix can be used for frothing when a gas such as fluorocarbon 12 is used as the high velocity gas stream or it can be used for conventional foaming if compressed air or nitrogen is used as the mixing gas. This is a useful system where quality requirements are average and the product is confined in a metal or plastic envelope.

Helix Mixer

A term describing the mixer used with the helical spiral mixing technique. The phrase is somewhat ambiguous since many of the rotating impellers are machined into a helical spiral shape. In order to avoid confusion it should be specified as a stator or non-rotating helix.

High Rise Application

High Shear Mixer

A mixer blade or impeller of the general type that mixes primarily by smearing multiple thin films of chemicals together in a high-speed close tolerance device. Generally associated with this type is a high mixer drive motor power loss and the transfer of a large amount of mechanical energy to the chemicals in the form of heat.

Hold Tank

A term sometimes used to describe storage tank(s) in which stable premixes are made and then held until the material is required to be transferred to the "run" tanks on the machine.

Hold-Up (In The Mixing Head)

The actual volume of chemicals in passage or in transit through the mixing chamber during mixing operations. This is usually not the total volume of open space in the mixing chamber, since centrifugal force generally keeps the center area open. Any built-in pumping features of the impeller will slow or speed the passage of the material through. Hold-up can only be increased if the mixing chamber is partially empty to begin with. With pumping type impellors, hold-up is rarely increased significantly by reducing the diameter of the discharge orifice.

Horizontal Cutting

The practice of cutting foam when the cutting portion of the blade of the saw is in a plane parallel to the horizon. Special rotary bandsaw mechanisms are most commonly used for this purpose, although hot wire cutting devices are also used.

Horizontal Pour

The practice of pouring large panels of urethane foam (particularly rigid foam) when the mold or void to be filled has its two largest dimensions form a horizontal plane. This has the advantage, when anisotropy is present, of having the greatest compressive strength of the material in a direction that supports the external skins.

Hot Wire Cutting

The practice of cutting foam by means of an electrically heated wire held taut between two posts with the help of a spring tensioning device. This has the advantage of eliminating dust and can be installed in multiple levels so that an entire Block can be cut in one passage. Disadvantages are the tendency towards rather slow production rates, the variability of response of different types of foam requiring critical adjustments, the possibility of unpleasant odors, and the ever-present possibility of fire. (The wire is maintained at 1200° F.)

Humid Aging

An accelerated aging test under conditions of high humidity and temperature. The Test Method is described in ASTM D 1564-63T under steam autoclave test.


A system in which energy is transferred from one place to another by means of compression and flow of fluid (e.g.. water, oil).

Hydraulic Drive Mixer

A hydraulic drive motor for the mixing head in which the motor segment is head mounted and the power unit is remotely located in order to decrease the total weight of the mixing head installation. This also provides variable speed adjustment.

Hydraulic Drive Traverse

A spreading device of the type that can be used on continuous slab production lines, utilizing a hydraulic drive mechanism.

Hydraulic Mixing Head

A mixing device in which the primary cause of mixing is the turbulence created by the interference of the streams of liquid components with each other as they are introduced into the mixing area. This is also called a fluid jet impingement mixer.

Hydrolytic Stability

A term which refers to the ability of the foam product to withstand hydrolysis or dissociation by water under conditions of constant exposure. The humid aging Test Method was developed in an attempt to measure this.


Water repellent.


An affinity for water. Hydrophilic foams are more absorptive and generally make better sponges.

Hydroxyl (OH) Group

The combined oxygen and hydrogen radical that forms the reactive group on polyols.

Hydroxyl Number

See OH number.


in the sense used in the foam industry, a term which refers to the decay in strength properties under continuously applied load. A typical example of this would be in the determination of RMA values where the test specifies that the reading must be taken at an exact time interval after the application of the load in order to assist in obtaining a reproducible value, since the values drop continuously.

IFD Value

A shortened form of Indentation Load Deflection value, formerly known as RMA value. A series of readings would be used to make an IFD curve, a single specified reading such as the 25% IFD value would be used for direct comparisons. The Test Method is described in ASTM D 1564-63T.

IFD (65/25) Index

A ratio of the 65% compression value divided by the 25% value. This ratio or index indicates, to some extent, a more or less linear relationship between readings taken to form a resilience (IFD) curve. Index readings above 2.00 are usually considered good for urethane foam; while index readings below 1.75 are considered poor, and the foam can be described as 'boardy'.


A term used to describe the power driven mixing blade or rotor that is used to mix urethane components in a mixing head.

Impeller Housing

The shell surrounding the impeller and forming the outer limits of what is commonly called the mixing chamber. This is often readily removable for cleaning purposes. It may be smooth, grooved, or baffled.

Indentation Load Deflection

See IFD Value.


A measure of the stoichiometric balance or the relationship between the equivalent weights of the combining substances. In the case of urethane foam, this is the relationship between the equivalent weights of the isocyanate materials on the one side and the water and polyol equivalent weights on the other side. An Index of 100 indicates that both equivalents are equal or ‘balanced'. An Index of 95 indicates that there is a 5%shortage of isocyanate while an Index of 105 indicates a 5% surplus of isocyanate. A slight theoretical excess of isocyanate, usually 3-5%, is common practice, particularly with flexible foams. Other levels may be specified with special formulations.

Infinite Flow-Rate Control

The ability to control the rate of flow of one or more of the components to any amount desired. This is very ambiguous, since maximum and minimum limits must usually be specified to obtain the desired tolerances of Accuracy. Some degree of infinite control can be achieved with pressure pot metering, pneumatic drive motors, hydraulic drive motors, variable pitch sheaves, variable contact cones, etc. With some of these a wider range of control is achieved by the sacrifice of stability at a specified setting.


A substance that slows down chemical reaction. Inhibitors are sometimes used in certain types of monomers and resins to prolong storage life.

Initial Spot

A spot of off-quality foam located at the point where the first amount of liquid mixture was deposited. This can be due to improper pressure balance, unbalanced discharge velocities, extreme differences in viscosity, oversized mixing chamber, etc.

Initiation Time

A synonym for cream time. In frothing it usually refers to the delay time between the initial expansion and the beginning of the secondary or final expansion.

Injection Molding

A molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity which gives the article the desired shape.

In-Line Cutters

Cutting machines that have been installed directly in a continuous slab foam production line so that handling of the foam is minimized. Some manufacturers trim only the top, bottom, and side skins at this point; others go all the way and make all the cuts in-line.

In-Line Heat Exchangers

Heat exchangers that have been installed in the flow circuit so that the pump must be operating for the exchanger to be effective. This serves to differentiate between this type and the blanket type units that are wrapped around machine tanks.

In-Line Mixer

A special mixer that has been added to one of the flow circuits in order to premix one or more of the minor ingredients into one of the major component streams. A common use is to premix the silicone and air into the polyol stream at a point just prior to the final mixing zone.


A word used to describe the entire foam producing mechanism after it has been placed into its operating environment and provided with all the services required.


An instrument utilized to determine the tensile, compressive properties and other mechanical properties of foams.

Integral Skin Foam

A molded urethane foam product having a dense, tough outer foam skin and a relatively lower density core. The product is achieved in a single pour through a combination of chemical and mechanical aids.

Interlocked Systems

The practice of using a single power source to drive two or more fluid metering system. Each fluid metering systems would be independently variable in output to provide for setting an exact ratio between components , but changing the speed of the master drive motor would change the total flow rate without disturbing the ratio. This is also called a 'master-slave' system.

Internal Mix

The practice of mixing the various components inside a mixing chamber or housing and then discharging the mixture through one or more discharge ports. This is usually a more efficient mixing device than an external mixer but generally requires some solvent cleaning at intervals, dependent on the formulation, relative on time, duration of off times, etc. See external mix.

Interrupted Slab

A technique of pouring individual Blocks of slab foam in boxes of a definite length in order to make a wider and higher Block than would ordinarily be possible with the maximum flow rate of the machine available. This is possible because the box ends Block lateral foam movement, forcing the foam upward. On continuous slab the upstream side is always open, resulting in a required increase in conveyor speed to prevent the foam from falling over.


The foaming and swelling of a plastic when exposed to high surface temperatures or flames. It has particular reference to ablative urethanes used on rocket nose cones, and to intumescent coatings. It is extremely useful for fire resistance.

Intumescent Coatings

Coatings which when exposed to flame or intense heat decompose and bubble into a foam which protects the substrate and prevents the flame from spreading. Such coatings are used, for example, on reinforced plastic building panels.

Irregular Cells

A term used to describe foam that has a mixture of widely varying cell sizes and presents a very irregular appearance. This effect is sometimes caused by excessive air introduced to the mixing head and sometimes by certain chemicals added to the formulation.


The family name for those chemical compounds having one or more reactive NCO radicals or groups attached to the main molecule. Tolyene diisocyanate is the most commonly used member of this group.

Isolating Regulator

A regulator installed in a fluid metering circuit in such a manner that variations in downstream pressure do not affect metering accuracy. These are used in R-12 metering and catalyst pressure developing.


Any one of two or more chemical compounds having the same number of the same kind of atoms in their structure, but arranged in a different way. This change in structure sometimes affects the reactivity rate of the compound. In the case of tolylene diisocyanate a definite mixture of isomers is provided to the customer. The most commonly used mixture is an 80/20 blend. See isomer ratio.

Isomer Ratio

Is the ratio between the 2.4 isomer and the 2.6 isomer in commercial TDP. The 50/20 ratio of 2.4/2.6 isomer is the most common blend although the 65/35 2.4/2.6 isomer blend is also available.


Foam characterized by having the same strength proper- ties in all directions. To achieve this the rigid foam, in particular, would have to have 100% spherical shaped cell structure. In actuality the foam bubbles normally achieve a regular dodecahedron shape rather than Spherical. See Anisotropic for additional information.

Jacketed Tank

A term which refers to a tank having an additional metal shell, coils of tubing or resistance wire surrounding the inner tank in order to utilize the tank as a heat exchanger. The most common form of this is the separate outer shell through which steam can be introduced for heating purposes. Using this sort of tank for a chiller may cause problems with condensation. Insulation is sometimes used to gain efficiency.


See fixtures.

Jigs and Fixtures

See fixtures.

Jumper Hose

Usually a short length of hose needed when installing a device 'in-line' in the flow circuit of one of the components '. The existing hose is attached to either the inlet or the outlet of the new device as required, and the jumper hose then is installed between the other connection and the point of original attachment of the original hose.

"K" Factor

A measure of the insulation ability or thermal conductivity of the foam or material. In English measurements it is normally expressed as BTU’s / hour / square foot of area / degree F / inch of thickness, although some physical handbooks use a foot of thickness as standard. Since the measurement indicates positive heat flow, the relationship to insulating ability is inverse in that the higher the K factor, the poorer is the insulation and vice versa. Since the approved Test Method is so time consuming and expensive, many faster cheaper screening methods are in use.

Knit Line

A high density layer of foam indicating the joint between two adjacent pours of foam that did not flow together until after skins were formed. Under ideal conditions the various parts of a pour should flow together while still liquid, thus avoiding the formation of knit lines. This is a common occurrence with rigid foam.

Know How

A term which refers to the technical background information required in order to properly operate a specific process.

Labyrinth Mixing

A process similar to helix mixing, except the mixing zone is irregularly baffled instead of spiraled.


A term which refers to the delay or reduction in flow that occurs when a restriction in the flow circuit causes a build-up in pressure. This delay is particularly severe in flow systems that may have trapped air or gas in some portion of the circuit or in those systems that use accumulators or flexible hoses. When using 'on-off' mixing heads the pressure must be balanced between recirculation and mix or a surge or lag may occur.


The process of adhering 2 or more thin sheets of the same or different materials together to form a thicker product with possibly different properties. In the flexible foam industry in particular, it refers to the process of adhering thin sheets of flexible foam and fabric together. Two processes are in common use, flame lamination and Adhesive Lamination. A paper or foil covered rigid foam insulation board may be made by self-lamination of the chemical to the skins. Laminates are also made of rigid foams and plastics, metals, wood, and other substrates.


A term used to describe the problem of non-uniform or off ratio flows at the instant of starting or stopping the mix cycle in 'on-off' mixers. When complete control over flow conditions is not obtained, one material may 'lead or lag' the other material (s). The most common cause of trouble is a lack of proper pressure balance in the flow circuit between the mix cycle and the recirculate part of the cycle. Uneven velocities of discharge from the orifices may also cause trouble, as will one of the liquid streams being directed away from the impeller shaft while the other is directed towards the shaft.

Lead Time

A term occasionally used on flexible slab production lines to describe the distance between the mixer and the cream line. See cream line.

Let-Down Nozzle

The device, used in frothing, that provides the transition zone between the higher pressure in the mixing chamber and atmospheric pressure. It can vary in design from the readily adjustable (by pneumatic pressure) rubber sleeve type valve to a short length of hose that is squeezed by a C clamp. The object is to keep the mixture as a liquid as far down the nozzle as possible so that shearing of the bubbles is minimized. The discharge tip of the nozzle should be designed to minimize air turbulence so that a smooth 'rope' of froth is produced.

Let-Down Valve

That portion of a let-down nozzle that can be classified as a controllable valve. A let-down valve is usually employed in the production of froth foam.

Light Resistance

The ability of a plastics material to resist fading after exposure to sunlight or ultraviolet light. Nearly all plastics tend to darken under these conditions.

Linear Molecule

A long chain molecule as contrasted to one having many side chains or branches.

Liquid Filler

See diluent.

Liquid Seal

The technique of introducing the least reactive material, usually the polyol, into the mixing chamber at a point just below the mechanical seal, so as to lubricate the mechanical seal and act as a buffer to prevent direct contact of the seal with isocyanates. This is most useful with continuous mixers, it being difficult to maintain the liquid seal and ratio balance during rapid 'on-off' cycling.


See Block.


A term used to describe a long narrow Block of foam that is to be 'peeled'. See peeler.

Loose Skin

A phenomenon in molding in which the skin of the molded article is a loose intact film. This is normally caused by excessive movement or flow of the foam after gelation is too far advanced.

Low Pressure Laminates

In general, laminates molded and cured in the range of pressures from 400 psi down to and including pressures obtained by the contact of the plies.

Low Shear Mixing

A mixing technique whereby the liquid components are mixed primarily by rolling and stirring the chemicals in a mixing chamber of relatively large volume. Power loss and mechanical energy transfer in the form of heat are generally quite low. The pin type mixer is generally described as a low shear mixer. See high shear mixing.

Low Temperature Boiling Solvent

See fluorocarbon and fluorocarbon blown foam. Although the term generally refers to the fluorocarbon family, there are other materials that may be used such as methylene chloride, etc.


A device installed in an air line feeding a pneumatic device (air motor or piston), requiring small amounts of lubricant for best performance and service. The device meters the required amount of lubricant into the air as it passes through on the way to the air motor or piston.


An abbreviation for diphenylmethane diisocyanate. 'Crude' MDI refers to polymeric isocyanates derived from MDI.


See cc.

Mn (Number-Average Molecular Weight)

The total weight of all molecules divided by the total number of molecules.

Mw (Weight-Average Molecular Weight)

The sum of the total weights and molecules of each size multiplied by their respective weights divided by the total weight of all molecules.

Machine Start-Up Service

A service provided by some machine manufacturers to start new machines in operation. The manufacturer provides an experienced technician who trains the customer’s personnel in the proper operation and maintenance procedures (usually on site). Since these machines are often rather complex, the service is quite valuable. A rule of thumb often quoted is that 'proper operation is 50% of the profits'. Sometimes the service is included in the cost of the machine; at other times it is extra.

Machine Tanks

Those tanks that form a part of the operating system of a foam machine, usually mounted on the machine frame with the metering pumps either inside or directly beneath.

Manual-Automatic Selector Switch

A switch, included on the control panel by some machine manufacturers, that permits the operator to choose between automatic dispensing controlled by the timer or manual control timed by the operator.

Manual Solvent Flush-Squeeze Bottle Type

A term which refers to a plastic squeeze bottle filled with solvent such as methylene chloride, which is used to force solvent through the mixing chamber after operation.

Manual Solvent Flush, Valve Type

A term which refers to a permanently connected solvent flush system that requires manual opening and closing of a valve. The solvent may be supplied by a pump or pressure pot. A manually operated air flush may also be included.

Mass Effect

A term which refers to the influence that the total amount of chemicals poured has on the density, cure time, etc. A small pour generally requires a higher catalyst level and a much more careful control of the environment than does a larger pour in order to achieve the same properties. The 'surface to volume ratio' of the mold and the mass of the mold also has an influence on foam properties.


A term sometimes used to describe the mixture resulting from premixing as many minor ingredients as possible in with the polyol‘ in order to reduce the final number of components ’ to the lowest possible level or to have time to blend efficiently a chemical that is not very miscible with the polyol. See premix.

Master-Slave Drive System

Materials Producer

A term used to describe the basic chemical supplier, sometimes called 'raw material supplier'.

Material Tanks

An ambiguous term sometimes used to refer to the machine tanks built into or onto the metering system and sometimes used to refer to the material storage tanks in which bulk chemicals are stored until needed.


That material within which something originates or takes form. In the case of urethane foam the bubbles originate within a liquid matrix.


A term used in the USA to describe the cushioning material applied to a bed in order to make it more comfortable. A single bed mattress, in the USA, generally measures approximately 39 inches wide by 72 inches long by 4 inches or more thick, although there are many variations of this. A double bed mattress, in the USA, generally measures 54 inches wide by 72 inches long by 4 or more inches thick, again with many variations. Other countries have different names and different dimensions for this article.

Mechanical Traverse Drive

A drive system for mixed liquid spreaders or traversers that takes all reversal thrust directly on gear teeth, screw threads or some other non-shock absorbent device. This type of drive system generally has a greater maintenance problem than the pneumatic or hydraulic type.

Mechanical Mixing Head

A mixing device in which the primary cause of mixing is a power driven rotor or impeller which, by its speed of rotation and configuration, imparts turbulence to the fluids as they enter the mixing zone.


The repeating structural unit of any high polymer.

Metal Belt Conveyor

A particular type of metal surfaced conveyor in which each slat interlocks with its neighbor in such a manner that a chain link is formed across the entire width of the conveyor. This type is often used for continuous slab foam manufacture.

Metal Slat Conveyor

A type of metal surfaced conveyor used in the foam industry in which the metal slats are supported at each side of the conveyor by a chain and are not themselves interconnected as in the metal Belt Conveyor described above.


See positive metering. The term is also used to describe the practice of collecting the simultaneous flows of the various components in individual cups for definite time periods in order to check the calibration of the machine.

Metering Ports

The discharge orifices through which the final components are introduced into the mixing chamber. These may or may not be replaceable to assist in balancing pressures. Pressure balancing is very important to good molding and readily replaceable tubes are very important not only for start-up but also for maintenance cleaning. See metering tubes.

Metering System

The pumping system used to accurately control the flow of the liquid plus all the hoses, valves, gauges, and piping needed to make a complete flow circuit.

Metering Tubes

The interchangeable tubes used as discharge orifices in those machines designed for ease of pressure balancing. See metering ports.

Methylene Chloride

A chlorinated hydrocarbon that is most commonly used as the cleaning solvent in the urethane foam industry. It is the most effective of the cheaper, non-flammable solvents. Many other solvents are more or less effective and can also be used. Flammable solvents should not be used.


A term which, in the rubber industry, refers to a roller type mixing device that is effective with mixing very high viscosity materials such as gum rubbers and elastomers. In the paint industry as 'Ball Mill', it refers to a rolling type mechanism that revolves a drum in which pigments and powders are dispersed into a resinous medium by means of heavy pellets also contained in the drum. A 'hammer mill' is used to produce finely divided pieces of flexible foam from flexible foam trims. See crumb.


A mechanical device capable of mixing two or more materials together homogeneously.

Mixer, Helix or Helical Spiral

Mixer, Housing

Mixer Hydraulic

Mixer, Mechanical

Mixer, Spray

Mixing, High Shear

Mixing, Low Shear

Mixing Chamber

The section of a mixing head in which the final. combination of the ingredients occurs. It is usually that section contained within the impeller housing.

Mixing Chamber Port

A term occasionally used to refer to a metering port.

Mixing Head

A mechanical device capable of mixing two or more materials together homogeneously in one passage through the mixing zone, It may include valves, bearings, motor, etc. See mixer and Batch Mixer.

Mixing Head Hold-Up

See hold-up.

Mixing Head Mounted Drive

Mixing Zone

The portion of a mixing chamber in which mixing is actually accomplished. Normally the mixing zone is around the outer perimeter of the impeller.

Modified Total Prepolymer

A total prepolymer system that has been modified by diluting the catalyst solution with plasticizers, fire retardent Additives or even a portion of the original or other polyol. This serves the purpose of changing the ratios from about 97/3 to approximately 80/20 and consequently improves the tolerance or ease of handling of the formula , particularly at very low flow-rates.

Modulus of Elasticity

The ratio of stress to strain in a material that is elastically deformed. moisture vapor transmission-the rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.

Mold Liners

Thin shaped films of plastic or treated paper that fit smoothly into the mold cavity and are used in place of mold release. The liners may or may not form the finished surface of the molded article. Vacuum formed vinyl and ABS skins are often used.

Mold Packing

A term which refers to the slight excess of the actual foam quantity poured into the mold over that actually required to fill the mold under ideal conditions, particularly for rigid foams. The excess usually is set at some point between 5% and 15% over the exact amount required. This extra material serves as a buffer to absorb slight changes in material temperatures, mold temperatures, distribution of materials, etc., and also seem to aid in reducing rejects caused by skin defects. It is also said to aid in improving load bearing properties of the foam. Flexible foam molding techniques do not generally employ packing in excess of 5% due to the formation of hard spots under excessive internal pressure conditions.

Mold Release Agent

One of many chemical compounds which, when applied to the mold surface, serve to prevent the cured foam from sticking to the mold. Because of the many variations in the formulations used in urethane foam, no one class of releases seems to have a clear advantage over others. Classes of releases that have proven useful include telomers, silicones, waxes (both synthetic and natural), and soaps of various sorts. One of the more useful. concepts used for flexible foam release involves the use of a microcrystalline wax which is a solid at the temperature of the mold during pouring, but melts during curing so that the final release coating is a liquid film.


The practice of pouring the mixed liquid foam ingredients into a shaped cavity, closing the cavity, allowing the foam to expand and cure to the handling point, and then removing the foam article from the cavity. Good molding practice usually dictates control over the temperature and quantity of the foam ingredients used, the temperature of the mold surface, the distribution of the liquid in the mold, the cure temperature, the cure time and the venting of the displaced gas from the mold.


A term used by some continuous slab process companies to describe the individual(s) that supervise the production of the foam by direct observation of the foaming process, the instruments, the final foam, etc.


Moon Cratering

See cratering.


A term suggested by some to be used in the foam equipment field to describe those machines that are portable only with the use of many men or heavy lifting equipment.

Multiple Component

A term used to describe a formula or machine that requires handling two or more liquid ingredients at the point of final mixing.

Multiple Pour Technique

A technique used to overcome deficiencies of formulation or equipment in the filling of molds, particularly thin, high rise cavities. If a single pour in the mold cavity would deform the walls or would result in an uneconomically high density, the wall would preferentially be poured in layers. The foam rise in each layer is restricted to that amount associated with the best properties in the foam. Usually each layer is permitted to harden before adding the next, If the equipment does not have sufficient capacity of flow rate to fill the cavity in one pour without seriously damaging the rising foam, then the cavity must also be poured in layers. The height of each layer would then be determined by the flow rate of the machine.


The chemical symbol for nitrogen. Nitrogen is often used as an inert, dry gas blanket over the chemicals in the otherwise sealed chemical tanks in order to avoid problems with moisture contained in atmospheric air.


The chemical symbol for the isocyanate reactive radical or group.

NCO/OH Ratio

Is the ratio between the available isocyanate groups and the available hydroxyl group in a foam formulation. When referring to a complete foam formula , the term index is more commonly used. The isocyanate index is the NCO/OH ratio x 100. When referring to a prepolymer formula , it is more common to refer to the NCO/OH ratio.


The chemical abbreviation for n-ethyl morpholine, an Amine catalyst used in foam formulations.


The chemical abbreviation for n-methyl morpholine, an Amine catalyst used in foam formulations. It is slightly more volatile than NEM.

Nitrogen (Gas) Blanket

See N2.

Nominal Throughput Range

A term used by foam machine manufacturers to indicate a throughput or flow rate capacity that a particular machine was designed to handle with 'normal' formulations. Because of the extreme variability in the type of chemicals that can be used to make urethane foam, not all formulations process the same way on the same machines so that a machine capable of metering and mixing 30 pounds per minute of a 1000 cp viscosity material might only be capable of metering and mixing 10 pounds a minute of a 20,000 cp viscosity material.


A rather ambiguous term permitted to be applied to certain formulations of foam fulfilling certain conditions of test outlined in Test Method ASTM D 1692. In actual use particularly in confined areas, some, but not all, of the foams with this label may burn quite rapidly; therefore, if a foam is required that will not contribute fuel to a fire under any circumstances, a different method of test must be used. Since the term is misleading, it should not be used without precise statement as to the conditions involved.


A term generally used to describe a nozzle or mixer that does not become plugged in use. The term, when used by itself, should be taken to mean non-clogging 'in normal use with a normal formulation'. Non-clogging under any condition of use has not been demonstrated as yet by any device.

Non-Recirculate System

A metering system in which the metered chemical flow goes directly to the mixing head and out. During off periods, the flow of chemicals is stopped. The term is primarily used to describe those systems in which the metering pump itself is stopped, although it is occasionally applied to systems in which a valve is used to stop the flow to the mixing head and a pressure relief valve bypasses the flow to another location until the valve is reopened. See recirculate system.

Non-Rotating Impeller

See helix mixing.

Non-Valved Components

A term used in working with 'on-off' mixing heads to describe those components introduced to the mixing zone through a port that is not controlled by the 'on-off' valve. For example, a 3 component mixing head of the 'on-off' type would normally have 3 valved ports that were simultaneously switched plus 2 additional non-valved openings that would normally be used for solvent and air but could be used for other components such as fluorocarbon 11and colors.


A very general term used to describe the discharge opening or tip of the mixing head or spray gun. It is occasionally applied to the entire mixing head, particularly if the device is hand-portable.


A term used to describe assistance applied toward the generation of many small, uniform bubbles as opposed to the formation of a few large bubbles in the same volume of space. As currently understood under chemically pure conditions it requires more energy to create a new bubble than it does to make an existing bubble larger, consequently without assistance foams would try to form the largest possible bubbles. The assistance normally given, as described by the term nucleation, may involve the addition of special molecules, small rough particles, dissolving high vapor pressure gas in the liquid, forming tiny gas bubbles mechanically throughout the liquid, or may even involve a shortening of the time interval during which bubble formation occurs in order to minimize migration of gas molecules toward existing bubbles.

Number of Components

Is a rather ambiguous term used to indicate the number of separate fluid streams that enter the final mixing zone. It should normally be qualified in use to avoid confusion. For example, a 4 component 'on-off' mixing heads would normally be expected to have 4 openings into the mixing chamber that are controlled by the 'on-off' valving when, in actual fact, many mixing heads have 2 additional openings that are not controlled by the valve. Contrarily, a 4 component continuous mixing head may have just the 4 openings with no additional ports.

"O" Ring

A seal or gasket that has a round shape (like the letter O) and a round cross section.

OH Groups

OH Number (Hydroxyl Number)

Is the number of milligrams of KOH (potassium hydroxide) that is chemically equivalent to the activity of a specified weight (in grams) of the polyol. This number is used in calculating the equivalent weight of the water and polyol for the purpose of determining stoichiometry or index of a formula .

'On-Off' Mixing Head

A mixing device with a special valve section capable of dispensing an accurate amount of well mixed foam ingredients at periodic intervals. Start and stop should be virtually instantaneous with no variation in foam quality from the first drop to the last drop. Time 'on' and 'off" can be controlled by a wide variety of methods ranging from manual movement of a valve lever to automatic timer control of an actuator for the valve section.

One-Roll Paper Feed System

A system of paper handling for the lining of conveyors in continuous slab foam processing, based on a single roll of paper that is wide enough to form the bottom plus both sides of the trough. For 84 inch wide conveyors rolls of paper as much as 13 feet wide are required. Not all styles of paper can be purchased in these widths, particularly release papers; and wrinkling problems may occur if tensioning of the roll by the paper mill has been poor or if paper alignment is bad. Because of this many manufacturers use the more complex three roll paper feed system.

One-Shot Foaming System

A system for the production of urethane foam in which none of the isocyanate portion has been prereacted with any portion of the polyol prior to final mixing. A minimum of 2 components are required, and more than 2 are often used. The ratios between the two major components are normally somewhere between 50/50 and 70/30 for most formulations.

Open Cells

A term applied to foam cell structure characterized by interconnecting cells or bubbles. Flexible foam should be 100% open celled for best quality. This characteristic is difficult to measure directly in flexible foam, and several indirect tests are in use that measure the air flow through a sample of a certain size and thickness.

Open Molding

A term which refers to the practice of pouring into a cavity having a closed bottom and sides but an open top. The mold may be shallow or deep. It is generally not the most economical way to mold a product but may have an Application where minimum internal mold pressures are required.

Organotin Catalysts

Are a family of urethane foam catalysts that are noted for their rather specific influence on the gelation reaction. By properly combining an organotin catalyst with an Amine catalyst such as triethylenediamine, a good balance between blowing and gelation reactions can be achieved. The most commonly used catalyst of this type is probably stannous octoate although dibutyltin dilaurate and others of the dibutyltin group are also used.

Overall Block Density

A term which refers to the practice of determining the density of the uncut foam Block in order to provide data for process analysis. By knowing the density at this point, an accurate gas loss value can be computed, and trim loss can be more easily calculated on a weight basis instead of on a volume basis. Not all foam producers bother with this intermediate step. To avoid guessing, Block height is usually averaged by taking the maximum center height of the crown and subtracting % inch.


The amount of unwanted excess of foam that has been poured into a mold either intentionally or unintentionally. See mold packing, and packing.

Overpressure Cut-Off Switch

A switch actuated by movement of a diaphragm or bourdon tube located near the pump in the flow circuit and arranged to cut off the power to the pump drive motor. This device protects the fluid circuit against damage from over pressurization. Other types of Overpressure protection devices are available such as pressure relief valves and blowout disks. See cut-off switch.

Overpressure Switch

A shortened form of overpressure cut-off switch.


A term in urethane foam spray Applications which refers to the particles of atomized material that hit outside the intended target area. With some equipment, formulations, and environmental conditions this may amount to as much as 50%of the material sprayed; with others it may be as low as 5%. Usually the finer the atomization the smoother is the surface of the foam applied, but the higher is the percent of overspray.


The addition of oxygen to a compound or the reduction of hydrogen.


An acronym which is a registered trademark representing one of the polymeric isocyanates that are used in the manufacture of one shot rigid foam, particularly flame resistant formulations where high char strength is desired. PSI-the abbreviation for pounds per square inch but does not indicate if the reading is by gauge or is absolute. PSIG-the abbreviation for pounds per square inch, gauge. Absolute readings at sea level would be 14.7 pounds per square inch. higher than gauge readings.


An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH7 - acid solutions being under 7 and alkaline solutions over 7. Accurate pH meters are commercially available.

Package (d) Unit

A unit that needs only to be supplied with services and filled with chemicals to make foam. The term is somewhat ambiguous, since it is used to refer to small individual metering and mixing units as well as to giant continuous slab process lines complete with all accessories required to make the final product.


A term which can refer either to mold packing or to the seal around the rotating shaft of some pumps or mixers.

Paper Handling Device

An overall description given to an apparatus on a slab foam production line that cradles one or more rolls of paper, allows the paper to unwind over a special framework at the proper tension, shapes the paper to the form desired, smoothes and flattens the paper on the conveyor, and may or may not unwind the paper from the foam slab.

Paper Shaping Device

That portion of a paper handling device that shapes the paper into the desired form and holds it there until the foam has enough strength to support it without assistance.

Paper Unwinding Device

A system of mechanically peeling the paper from the slab of foam as it moves past the unwinding station. It generally consists of a spindle at each side of the conveyor driven by a device producing constant torque rather than speed, and a roller device beneath the conveyor driven by the same or similar type drive motor. It may or may not be included under the general heading of paper handling system in a machine description.

Partial Prepolymer

Refers to a system for the preparation of urethane foam in which all of the isocyanate is prereacted with a small part of the polyol at some time prior to the introduction of the final components into the mixing chamber. This prereacted intermediate (partial prepolymer) may be prepared in a very complex manner in expensive equipment or it may just be poured together in a tank or bottle, mixed briefly and allowed to stand overnight. Foam prepared from a partial prepolymer can have superior properties to one shot foam but is usually more expensive due to the extra processing. Ratios between the two major components vary from about 50/50 to about 70/30. This is also known as a quasi-prepolymer or semi-prepolymer system.

Peak Rise Point

The point on a continuous slab foam process of maximum foam rise or height. Because of cell rupture there is usually some settling or subsidence of the foam beyond this point.

Peelable Quality

A term used to describe foam in which the cell structure is so uniform that when it is peeled or split to a thickness of as little as 1 millimeter, no noticeable variations in cell size or structure appear. To achieve this goal stringent control of all mechanical, chemical, and environmental variables is usually required.


A term used to describe a mechanical cutting device that is capable of slitting or peeling a continuous sheet of foam, as little as 1 millimeter in thickness, from the circumference of a round log shaped piece of foam. The technique is similar to that used to peel veneer from a wooden log. The cylindrical foam logs are sometimes trimmed from long Blocks of foam, with a square cross section that have been bored to accept the mandrel of the peeler. More recently techniques of foaming continuous round sections have been developed. See pre-peelers.

Peeling Cutter

See peeler.

Percent Set Test

Permanent Set

The increase in length, expressed in a percentage of the original length, by which an elastic material fails to return to original length after being stressed for a standard period of time. In flexible foam this generally is related to loss of height of a cushion in service.


The rate at which a liquid or gas can penetrate into or through a material, in this case foam. It is primarily of interest for water vapor or carbon dioxide gas permeability of rigid foams used in insulation Applications since either material reduces the effectiveness of the foam. See water vapor permeability.


A somewhat ambiguous term applied, in the USA, to a wide variety of small cushions used in many different type Applications. It usually is preferable to qualify the term with a more descriptive adjective such as head or sleeping pillows for those used on beds to support heads, decorator or throw pillows for those colorful and variously shaped cushions used to decorate furniture, etc. The original definition in the USA was limited to "something that cushioned and supported the head" but recently the meaning has broadened, perhaps in response to an awareness that Europeans used the word in a much different way.

Pin Impeller

A rotating mixing blade generally characterized as having a straight, relatively sturdy, central shaft parallel to the direction of liquid flow and a series of smaller, round, square or hexagonal shaped "pins" mounted on the central shaft at right angles to the central shaft and generally perpendicular to the liquid flow. There are many variations of this involving pin mounting angles other than 90 degrees (different diameter pins, different quantity of pins, different spacing between pins, etc). It is usually classed as a low shear mixing device.

Pin Mixer

A mixing head utilizing a pin impeller.


(n.) One of many high polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture every plastic is capable of flowing, under heat and pressure, if necessary, into the desired final shape. (a.) Made of plastic; capable of flow under pressure or tensile stress.

Plastic Deformation

A change in dimensions of an object under load that is not recovered when the load is removed; opposed to elastic deformation.


Various chemicals used as Additives in a formulation that generally serve to increase the flexibility of the foam structure. In flexible foam they can be used in some formulations to give a softer, more rubbery feel to the foam. In rigid foam they can be used to overcome extreme brittleness or friability where heat distortion is not critical.


A term used to describe the flat spot in a compression-deflection curve of a flexible foam that can be classified as 'boardy' or possessing 'boardiness'. A 'wide plateau' would indicate a very boardy foam. See IFD Index.

Pneumatic Drive

A term better known as air drive or air actuated. There are three different types classed as linear actuating pistons, vane type rotary shaft and piston type rotary shaft. Properly designed into a mechanism, air drives can be useful. As an example, pneumatic drive of a traversing mechanism provides two design features that are not present in any other type: pneumatic cushioning of the reversal to avoid metal fatiguing shock waves, and complete elimination of the heat produced by the absorption of the energy involved in reversal of the mechanism (the hot air is immediately discharged).

Pocket Blows

Tears or rips in the foam, approximately the size of a man’s hand, having smooth walls that are separated from each other. They may occur in the side or the interior of the foam slab.


A measure of the specific viscosity of a fluid. It is measured by the force required to move one plate in relation to another plate when the space between is filled with the fluid. A material with a viscosity of 1 poise requires 1 gram of force to move the plate 1 centimeter in 1 second. Since most of the fluids used in urethane foam have viscosities that vary with the temperature, any statement regarding the viscosity of these fluids must be qualified with the temperature of the hid at which the data was taken. centipoise, which is 1/1OOth of a poise, is more commonly used in the foam industry particularly since water is approximately 1 centipoise at 20 degrees C and thus provides a physical comparison with which we are all familiar.


A term used by some to describe the polyethylene cone shaped nozzles with different orifice sizes that are used to control the diameter and shape of the liquid stream being discharged from the mixing chamber of a urethane foam mixing head.


Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized by the presence of -C-O-groups in the molecule. This type of bond is more susceptible to attack by water (hydrolysis) than is the single oxygen present in the polyether type. Polyester polyols are generally more expensive, in the USA, than polyether polyols.


Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized as having ether groups -C-0-C-in the molecule. This type of molecular joint is less susceptible to hydrolysis than the type characteristic of polyesters. In general polyethers are less expensive than polyesters in the USA.

Poly Isocyanates

Isocyanate compounds having more than one isocyanate (NCO) group attached to the molecule. See functionality.


A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g., polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.

Polymeric Isocyanates

Is generally used to refer to those isocyanates containing products that consist of a mixture of isocyanate compounds containing more than two isocyanate groups in the molecule. This type is being widely used in the rigid foam field where good heat resistance and high char strength is required. This type of isocyanate reacts with polyol with less heat generation than with 'pure' diisocyanates; hence there is less tendency for scorching of the foam.

Polymerization Reaction

The chemical reaction during which larger molecules are being created by the joining of smaller molecules. If polymer chains are linked by chemical bonds to form a network, a cross linked polymer results. Flexible foams possess a lightly cross linked structure while rigid foams possess a highly cross linked structure. Proper choice of the base chemicals and the formula can result in a product with any desired degree of flexibility or rigidity.


Is a chemical compound with more than one reactive hydroxyl group attached to the molecule.

Polyol Mix

The product resulting from premixing many of the compatible minor ingredients into the polyol component. This is usually done in order to reduce the final number of components required to be metered and introduced into the mixing head and to improve the Accuracy of the compounding when some of the minor ingredients would be difficult to meter individually because of very small quantities or very high viscosity. This also allows time to mix some materials that are difficult to mix in the short length of time available in the final mixer. This product is also called 'masterbatch' and 'premix'.

Polyurethanes (Also termed Urethane Polymers)

Are a family of chemical compounds that can be prepared by the reaction of an isocyanate containing material with a hydroxyl containing material. See polymerization reaction and urethane.

Pore Diameter

A term synonymous with cell size. It is primarily used in Europe.


An ambiguous word that is defined as meaning 'easily carried'. Many advertising brochures carry descriptions of machines labeled as 'portable' that can only be 'easily carried by a fork lift truck. To avoid misunderstanding it has been suggested by some that portable be used in connection with anything that can be easily carried by one man, and that the word moveable be used for anything requiring 2 or more men.

Portable Cutters

Small, lightweight cutting machines for foam or fabric that have 8 inch to 24 inch long high speed reciprocating blade(s). These machines are usually quite versatile and are convenient to use in cutting out complex shapes that have been ordered in quantities too low for economical die cutting.

Positive Displacement

A term which refers to those pumps that are so designed that substantially all of the material displaced from the suction side of the pump is delivered to the outlet side of the pump. In other words internal recirculation is at a minimum and what little there is, is constant over a fairly wide range of conditions. In normal practice some limitation in use is necessary. Under some conditions, a pump that is positive metering with a 1000 cps material, may slip rather badly with 100 cps material. Under other conditions, a pump that is designed to be positive metering with a 1 cps material may transfer enormous quantities of energy in the form of heat to material of 1000 cps.

Positive Metering

The ability to control the flow rate of a particular fluid to an Accuracy of approximately 1% of the total flow regardless of temperature or pressure fluctuations downstream from the metering device. This is difficult to achieve in normal practice at all times under any conditions. It can be achieved economically if certain design rules and limitations of use are practiced. There is a certain amount of ambiguity in the term since many piston pumps can be classified as positive metering for total quantity delivered, while the amount delivered per second may vary, and many gear or vane pumps can be positive metering both for total quantity delivered and for quantity per second delivered.

Positive Proportioning

A term which refers to the condition in which two or more fluid streams are positively metered with respect to an absolute standard and are maintained in an exact ratio with each other continuously.

Positive Tracking

A term used to describe the condition existing when the flow rate is changed in two or more fluid circuits simultaneously while still maintaining positive proportioning. For Accuracy positive tracking is normally stated as a plus or minus variation from a standard flow level and for a specific viscosity material.


A term normally applied to the period of curing after the foam product has been handled by removal from the mold or conveyor. In some cases accelerated curing (usually oven heating) is practiced in order to achieve some predetermined level of physical properties. Depending on the formula and the final product desired, this may be accelerated post-cure in an oven at temperatures between 250° and 300° F. or a room temperature post-cure over a period of several days. The term sometimes is used ambiguously to cover what is otherwise called 'After-Cure'. See pre-cure and After-Cure. post-cure oven-an oven in which post-curing is accomplished. To be completely effective the product to be post-cured in an oven must be placed in the oven with as little temperature loss as possible while in transit from the manufacturing area.


A term applied to the practice of reshaping a piece of foam by the Application of a combination of heat and pressure after it has been cut to the proper dimensions. It is usually performed on flexible slab foam when pleasing or intricate curves are desired, and the investment in foam molding equipment would not be practical.


The process of encapsulating or imbedding a device by pouring a casting compound into a cavity in which the device has been fixed and curing the compound in place, As a result the device is imbedded completely in a plastic polymer, either solid or foamed. The compounds are usually thermosetting and vacuum may be used with the solid polymers in order to avoid entrapped gases.


A term referring to the practice of pouring a liquid into a cavity and having it foam, fill the cavity, harden and cure without having to remove it from the cavity and without having to shape the product by cutting or sawing. The term is sometimes used interchangeably with potting, but potting is used more to refer to the solid or non-foamed pour-in-place.

Pour Pattern

The pattern formed by a liquid steam being deposited in a mold, in a cavity or on a conveyor. This is often quite critical.

Pouring Head

A mixing head designed only to dispense liquid mixtures.

Pouring Point

The position at which the mixed liquid is deposited on the conveyor in a slab process system.

Powered Conveyor

A conveyor having the moving surface powered by a drive motor. The term is used to differentiate between this type of conveyor and other non-powered types, such as roller conveyor and skate wheel conveyor.

Pre-cure (pre-curing)

A term normally applied to the time interval between pouring the chemicals into a mold and the time the product can be removed from that mold without damage to the product or the mold. This is also sometimes called 'stripping time' or "handling time'.

Pre-Cure Oven

An oven in which pre-curing is accomplished. This can be supplied with heat from any source that will raise the temperature of the mold quickly without damaging the foam product or the mold. This is a critical part of molding process and is usually the limiting factor in molded foam production rates. Types of ovens in use range from hot air circulating heat, powered by steam, gas, oil or electricity, to microwave powered units. Some are equipped with powerful 'fast heat' radiant units to increase the internal mold temperatures more rapidly.


A term normally applied to the technique of bringing molds or cavities to the desired temperature level prior to pouring. This is a fairly critical factor and must be accomplished with reasonable Accuracy and reproducibility for best quality control. Even the so-called 'cold molding' process requires some mold heat control for quality standardization.

Pre-Heat Oven

The oven in which pre-heating is accomplished.


A term often used synonymously with masterbatch or polyol mix to indicate the mixture resulting from blending many of the minor ingredients in with the polyol in an effort to reduce the final number of components or to allow more time for mixing or blending those chemicals that may not be readily miscible in the short period of exposure to the final mixing. See polyol mix.

Premix Tank

A term used to indicate tanks that are used for making batches of premix separately from the machine and also those tanks on the machine that are used in the premix flow circuit.


Specially modified cutting devices that round off the corners of Blocks of foam that are to be peeled so that very little time of the actual peeler is wasted in this time consuming operation. Actually, the major portion of the peeling cycle is spent in installing the 'logs' of foam and attaching the first amount of peeled material to the wind-up roll. Prepeeling may reduce this wasted time by as much as 50%.


A chemical intermediate used at times in the production of urethane foam. It is normally manufactured by prereacting all of the isocyanate material with part or all of the polyol. This can be carried out in a special reactor kettle or in a normal blending tank and is a means of building some properties into the final foam product that would not be there ordinarily. See total prepolymer, modified total prepolymer and partial prepolymer.


A technique used to secure more exact chemical metering when froth is to be produced. Usually special valves are installed between the pumps and the mixing head and the pressure generated by the pumps is increased to the value that would be present during the frothing pour by using this special valve to throttle the liquid flow. Metering or calibration of the liquid flow rates and ratios is accomplished while the pressure is at the artificially high level in order to minimize the effects of internal pump slippage on calibration. The valves are left in this position during operation. Pressures of 70 to 150 psig are normally maintained in the mixing head during frothing in order to keep the fluorocarbon 12 in its liquid phase during the mixing operation.

Pressure Balance

A term used to describe the condition existing in an 'on-off' fluid metering circuit when the pressure during the 'on' cycle is exactly the same as the pressure during the 'off' cycle. This condition is normally required for best quality foam production, as most commercial foam machines have rubber hoses in the circuit plus places that could trap gas and act as accumulators. Under these circumstances if the pressure were permitted to change, a surge or lag of material could occur immediately after switching 'on' (mix cycle) which would cause an imbalance in the stoichiometric ratio of the chemicals, and poor quality foam or 'initial spot' during at least a portion of the cycle would result. Generally the shorter the 'on' time, the more critical is the pressure balance, depending on the design and capacity of the impeller and mixing chamber.

Pressure Balance Valve

A valve located somewhere in the return line between the mixer and the tank and used to help in balancing pressures. In some cases this valve is built into the mixing head, and in others it is separate and located on the tank. For some materials, particularly isocyanates, the construction of the valve is important, and it should be of a type that does not accumulate small particles. In most cases a filter is installed just prior to the valve to ensure more trouble free performance. The closer the valve is to the mixing head, the better is the performance. regulators are sometimes used for pressure balance instead of valves.

Pressure Cut-Off Switch

Pressure Developing

A technique used to gain more positive control of metering when a water-thin (1 cp) viscosity liquid must be metered at extremely small flow rates. This situation is encountered often when total prepolymer systems are used for filling very small cavities. With this technique a special needle valve or pressure regulator is installed in the flow circuit of the catalyst system between the metering pump and the mixing head and as close to the mixing head as possible. A back-pressure (between the valve and the pump) of at least 5 psig is maintained at all times. Very small inner diameter metering tubes must be used in the mixing head to keep the system liquid full at all times, but they must not be so small as to cause the pressure to rise during the 'on' cycle.

Pressure Gauge

A device for measuring and indicating pressure. It is not safe or practical to operate a urethane foam machine without accurate pressure gauges in all flow circuits.

Pressure Introducing Device

Pressure Isolating Regulator

Primary Alcohol Groups

Are reactive groups present in certain polyol molecules. Primary alcohol groups react faster than secondary alcohol groups. Usually, the higher the percentage of primary alcohol groups in the formulation, the less catalyst is required for curing. The term 'primary hydroxyl groups' is often used interchangeably.

Prime Mover

A term used to describe the master drive motor and speed controller used with interlocked or master-slave systems.

Process Variables

Factors in the chemicals, the machine or in the environment that could change in such a way as to affect the quality of the foam. More than 50 have been identified and labeled in the production of flexible slab foam. Among these factors are such things as the control over metering stability, temperature of the chemicals, catalyst type and level, etc.


Proportional Limit

A term used by those concerned with testing work to describe the point at which an elastic modulus changes from a straight line function. This would normally indicate the elastic limit of the material beyond which permanent damage to the material structure would result. puddle-the practice of pouring all the mixed liquid material into one spot in a mold or cavity with no attempt to distribute the material.


A term occasionally used to describe a metering unit.

Pumping Impeller

A mixing blade designed to positively move the liquids being mixed through the mixing zone and through the discharge orifice by means of the force exerted by the pumping action designed into the mixing blade itself.

Quasi-Prepolymer (Quasi-System)



A shortened form for refrigerant 12 which is a neutral (non- trademark) name sometimes used to describe fluorocarbon 12, (dichlorodifluoromethane) a very low temperature boiling liquid commonly used as a frothing agent for urethane foam.


An abbreviation used to represent Rubber Manufacturers Association Test which is an indentation load deflection test used to rate cushions and mattresses for load carrying ability. The term is rarely used, the preference being for IFD test. The Test Method is described in ASTM D 1564-63T.

Rat Holes

A term which refers to the large, irregular, normally elongated gas pockets usually found in frothed foam. Their size can be minimized by careful manipulation of the mixing chamber pressure, the percent of R-12 used in the formula, the type of chemicals used, etc. They are also called worm holes.

Ratio Control

The ability to change and regulate the ratio or proportion between 2 or more fluid components . This introduces versatility to a machine, enabling it to be used with several different formulations. A fixed ratio machine can be built that will work with only one formula under precise operating conditions, but these are rarely requested. raw materials-a term often used to describe the chemical ingredients used in manufacturing urethane foam. The term is generally applied to the chemicals as received from the chemical manufacturers prior to any premixing.

Raw Material Manufacturer-(Also Called Materials Producer)

A manufacturer of one or more of the basic chemicals used in the urethane foam industry.


A general term that can be used for any of the raw materials or intermediates used in the manufacture of foam.

Reaction Balance

The balance between the relative reaction rates of gas generation (blowing) and gelation (polymerization). This is quite important in the production of urethane foam, as a formula with too rapid generation of gas may cause collapse or splits; while a formula with too rapid a gelation rate will become closed celled in the case of flexible foams, or may tear apart by internal cracks in the case of rigid foams. See blowing reaction, gelation reaction and polymerization reaction for further information.


Is a term used to describe the process of adhering small particles of foam (crumb) back together again to make a saleable cushioning product. Several processes are available, some using latex adhesives, others using a foaming adhesive based on the urethanes, some requiring heat to cure or to dry, others curing at room temperature, some producing an inferior product, others producing a product superior to 'virgin foam' in many ways. A typical Application of rebonded foam is for rug underlays.


A seldom used term describing a device used for spreading the mixed liquids in a uniform pattern in molds or on conveyors. They are also called traversers or spreaders.

Recirculation System

A term which refers to the practice of continuously pumping the metered fluids back to the machine tanks during the "off" portion of a foam production cycle. The 'on-off' valving in the mixing head serves merely to divert this continuously metered flow either into the mixing chamber or back to the machine tanks. There are three different degrees of recirculation defined as follows: Full recirculation all the way to the mixing head and back with little or no volume of non-recirculated material between the diverting valve and the mixing chamber, partial or short recirculation in which the diverting valve is located at some distance from the mixing chamber, resulting in a relatively large volume of non-recirculated material between the valve and the mix chamber, and non-recirculate in which there is no return line at all and the pump is either stopped during the 'off portion of the cycle or the pump is equipped with an internal bypass that operates when a valve is closed in the line between the metering pump and the mixing head.


A fluid control device usually consisting of a housing, a spring loaded diaphragm and a means for adjusting the spring tension. This can be used to control either the upstream or downstream pressure.


A term sometimes used as a synonym for hysteresis or sometimes as a synonym for the settling that occurs after peak foam use.

Remote Drive

A drive motor, usually for a mixing head, that is located at some distance from the mixing head itself and transmits power by means of a flexible shaft drive or some other method.


A powerful pleasant smelling chemical which is added to a formulation to mask the unpleasant odors sometimes associated with Amine catalysts or even the polyols on occasion. There are a wide variety of scents available and if used properly, reodorants can perform a valuable service.


The ability to produce the same result at repeated intervals. This is a very important consideration in buying chemicals or machinery, since lack of reproducible control over any production variable can result in the production of poor quality foam.

Resilience Value

A measure of the 'rubberiness' or elasticity of the product, in compression. One of the methods for measuring this is the 'Ball Rebound Test'.

Resilient Foam

Foam that has a very rapid recovery from extreme compression and a fairly linear increase in resistance to compression per inch or centimeter of penetration.


A term used as a general term describing the unsaturated polymers or monomers used in the paint industry, in particular those in the polyester family. It is occasionally applied to the polyols used in urethane foam.

Resin Heater

Is a heater, usually in-line, that is in the fluid circuit, (either polyol or isocyanate stream).


The process of removing residual membranes or cell windows from the foam structure so that only a skeletal web-like network remains. There are several techniques involved and there are many patents in the field.

Reticulated Urethane Foams

Very low density urethane foams characterized by a three-dimensional skeletal structure of strands with few or no membranes between the strands, containing up to 9701, or more of void space. They are made by treating an open-cell foam structure with a dilute aqueous sodium hydroxide solution under controlled conditions so that the thin membranes are dissolved, leaving the strands substantially unaffected. Ultrasonic vibrating is sometimes used to assist the solution process. These foams are used in filters for air-conditioners, automobile carburetors, air cleaning systems; and in acoustical panels, humidifiers and various household products.


Is the study of flow and deformation of matter.


Like structures formed at the joint between adjacent bubbles in a foam which becomes open-celled. The ribs are usually reinforced by the remains of the cell membranes in good quality foam.


See flow lines.

Rigid Foams

Those foam products which can be classified as having a firm stiff behavior and can be said to exceed their elastic limits with compressions or elongations greater than 10%. There are many other plastic based rigid foams than polyurethane foam. The most common of the other types are polystyrene foam, epoxy foam, polyethylene foam, phenolic foam, and urea-formaldehyde foam. Rigid foams may be thermoplastic or thermosetting.

Rise Time

The time interval between the liquid mixture being poured into the mold and the completion of expansion of the foaming mass.

Roller Conveyor

A usually non-powered conveyor that is constructed of a series of tubes suspended at each end by a shaft and bearings which are fastened to a rail on each side. The rails are parallel to the direction of movement; the axis of the rollers are perpendicular to the direction of movement, but the surface of the rollers rotates in the direction of travel when a product is pushed on top.


A slang word referring to the appearance of the froth being discharged from a letdown nozzle. When all variables are in proper adjustment, the discharging material often takes on the round slightly fuzzy appearance of a manila rope dangling in air.


A term sometimes used to describe a mixing blade or impeller.

Run Tanks

A term sometimes used to describe the machine tanks that form part of the metering system in order to distinguish them from bulk storage or premix tanks.

Run Time

The time during which the foam machine was actually in operation to make foam. Recirculation time is excluded.


An abbreviation used to refer to the Society of Plastic Engineers. This is a national organization of engineers working in the plastics industry. The executive office is located at 65 Prospect Street, Stamford, Connecticut 06902. many regional chapters cover The SPE Journal is the official


An abbreviation used to refer to the Society of the Plastics Industry. This is a national organization of companies and individuals in the plastics industry that is oriented towards developing industry standards and test methods, their Applications, and promotion of plastics as well as maintaining the proper public image.

Sack Factor

Sag Factor

Sandwich Panel

A composite structure intended to serve as a structural building panel for walls, roof, floors, etc., posed of at least three pieces, a low density case (a rigid foam) and two outer skins or surfaces. The major portion of the load bearing is intended to be accomplished by the two outer surfaces, while the inner core serves primarily to maintain the outer surfaces completely in parallel. schematic diagram-a drawing that illustrates the design and relationships of a machine, circuit or process in an abstract or symbolic manner bearing no relationship to its physical appearance or size.

Scoop Cutting

The technique of producing special cut shapes from Blocks or sheets of flexible urethane foam by variably compressing certain areas of a foam Block and cutting the foam while it is deformed. Foam soap dishes and variously shaped cavities that are used as shipping containers for light bulbs, glasses, TV tubes, etc., are among the many that can be made in this manner.


A term which normally refers to waste from a urethane foam manufacturing process that cannot be used. This term is often used to describe usable trim cuttings also. See trim. scraped surface heat exchanger-See heat exchanger, scraped surface.

Scraper Unit

A shortened form of scraped surface heat exchanger package unit.

Sealed Mixing Heads

A mixing head' with a built-in rotary seal on the impeller drive shaft and possibly an '0' ring seal around the mixer housing so that mixing under pressure, such as in frothing, may be accomplished without leaking the mixed materials into the bearing housing or other areas. For best results, rotary seals must be lubricated. The best arrangement appears to be a DOP circulation system. Another system, primarily useful in continuous processing, is the polyol lubricated seal.


Devices used to heat-seal sheets of foam together so that the 1000 to 2000 yd. rolls used by the laminated fabric industry can be built up, The sealers are usually mounted on the frame of the peeler between the cutting bar and the wind-up roll. Sealing is usually accomplished by a combination of pressure and a heated resistance wire.

Seat Cushions

Blocks of foam used for padding in chairs on which a person sits. They may be separate from the main frame of the chair or sofa or form an integral part of it. A Back Cushion, on the other hand, is leaned on rather than sat on.

Seat Pillow

A term used in Europe with the same meaning that 'seat cushion' has in the USA.

Secondary Alcohol Groups

Are reactive alcohol groups (CHOH), present in most polyol molecules. They are less reactive than primary alcohol groups. See primary alcohol groups.

Self Cleaning

The ability of a mixing device to so completely expel the mixed materials after an 'on' cycle that repetitive cycles can be accomplished without any clogging. In actual practice this is difficult to attain on an absolute basis since it is influenced by the cream time of the formulation, the length of the 'on' time, the length of the 'off' time, etc. Because of this some form of solvent flush is normally required either after each cycle or as long as after every four hours of use.

Self Extinguishing

The ability of a foam to stop burning after it has been started burning in a controlled manner. One of the tests used to determine this is Test Method ASTM D 1692. Caution must be used in applying the results of this test to actual Applications, since the sample is unconfined during the test, and flammable decomposition products are free to escape.

Self Skinning Foam



A term which refers to the relative ease of the daily manufacture of foam using a specific formulation. If all operating conditions must be exactly controlled in a very narrow band in order to make acceptable quality foam, the formulation is said to be sensitive or critical. If acceptable foam can be made day after day with only average control over the variables, the formulation is said to be tolerant.


The normal loss in height of the continuous flexible slab foam at a point just past peak rise. This loss of height occurs as the cell walls rupture and is a sign that the foam will be open celled. If the loss of height is excessive, splits may occur. If the loss of height does not occur the foam will normally be closed cell.

Shaping Saws

Cutting devices that can produce almost any special shape desired from a Block or sheet of foam. Some examples of this type saw are shoulder pad cutters, scoop cutters, convoluting cutters, breast pad or hip pad cutters, circular cutters and bolster cutters. sharp cut-off-a term which describes the ability of a mixing head to stop the flow of mixed liquids abruptly as soon as the valving mechanism cuts the flow of the chemicals into the mixing chamber. 'No After Drip' also describes the same condition. This condition is greatly dependent on the material viscosity and is almost impossible to achieve with low viscosity formulations.

Shear Resistance

The ability of a flexible foam to resist laterally applied forces (applied parallel to the foam surface). This has a bearing on the comfortability of the foam when used as a cushion and its abrasion resistance.

Shear Strength

The ability of a rigid foam to resist deformation when subjected to laterally applied forces (parallel to the foam surface). This is of interest particularly in sandwich panel work. The Test Method is described in ASTM C 273-61.


An ambiguous word used sometimes to describe cratering and sometimes to describe windows.

Shiny Foam

Foam with a high proportion of cell membranes (windows) that glitter from reflected light.

Short Recycle

Short (re) cycle valving-the valves or valving device used to recirculate the separate components on a short recycle system. They are usually similar to the valves used for full recirculation, but not always. See recirculation system.


The total amount of mixed liquid dispensed from an 'on-off' mixer during an 'on' cycle.

Shot Accuracy

A term which refers to the reproducibility of the total quantity delivered by an 'on-off' mixer in a specified time interval. An Accuracy of plus or minus 0.25% can be achieved with good quality equipment, depending on the formula and the size of the shot. As a general rule the shorter the time 'on', the greater the Accuracy problem.

Shot Cycle

A term which describes the total time spent 'on' and 'off' in a single unit of operation. Usually the time 'on' and the time 'off' are both identified. For example, 5 seconds 'on' and 10 seconds 'off' would completely describe a shot cycle.

Shot Cycle Timer

A timing device used for automatic control of a shot cycle. See shot size timer.

Shot Size Timer

A timing device used to control the duration of the 'on' time only. It has to be manually actuated for each 'on' cycle and has no control over the 'off cycle. The term is often used interchangeably with shot cycle timer.

Shot Timer

A term normally used as a synonym for shot size timer.


A mechanical device used to tear or rip foam trim pieces into very small pieces which can be used for filling dolls, pillows, etc., or for rebonding into cushioning products. They are also called grinders, hammer mills, etc. See crumb.

Shrinking (Shrinkage)

A term which describes the loss in size that occurs occasionally with foam products. Exothermic temperatures encountered in the interior of many foam products is often between 250° to 300° F. At this temperature the gas in the bubbles is exerting a higher pressure than it would at room temperature. In order to withstand this loss in pressure the cell walls must break, in the case of flexible foam, or the cell walls and structure must be rigid enough, in the case of rigid foam, to accept the pressure difference without collapsing. If a flexible foam has closed cells, it will shrink when it cools. If a rigid foam does not quite reach a truly rigid structure before cooling, the cell walls will either rupture, or, if the material is somewhat plastic, the foam will shrink in size. It is sometimes used as a synonym for settling in a flexible slab process.

Side Conveyors

Conveyors that are used as moving sidewalls on a continuous slab process conveyor. This is particularly applicable to rigid slab manufacture when the formulation has a tendency to gel prematurely and as a result exert sufficient pressure on non-moving sidewalls to lock the slab in place.

Side Cracks

Definite cracks in the foam with widely separated edges.

Side Splits

Horizontal tears or rips in the side of the foam Block. These splits are either horizontal to the plane of the foam conveyor or slightly angled. They may appear intermittently or continuously along the side of the slab. The edges of the tear are not separated to any large extent, and consequently the tears are often difficult to see. Two common causes are an excessive speed of the blowing reaction in relation to the gelation reaction and too steep an angle of rise.


Complex chemicals formed from a combination of silicon and organic groups to form polymers that exhibit surface active properties when used in urethane foam formulations. In general these compounds add stability to the liquid foaming mixture so that drainage (collapse of bubbles due to extreme loss of bubble wall thickness) is retarded and flow ability of the mass is increased. There are many different varieties that can be used; some contribute to fine uniform cell structure, while others increase the irregularity of the cell structure (for sponges).

Simulated Chamber Pressure


A term which describes the higher density outer surface of a foam article. See integral skin foam. The skin usually is the result of surface cooling. It can be eliminated by maintaining the outer surface of the part at the proper temperature.

Slab Foam

Foam made by the continuous pouring of mixed liquids on a conveyor generating a continuous loaf of foam for as long as the machine is operating. This type of foam would generally be classed as free rise or unconfined, although fixed side guides give the loaf a generally rectangular cross section with a slightly rounded top. A few installations have a top conveyor to aid in flattening the top surface so that a more nearly rectangular cross section is produced.

Sleeping Pillow

A term which in the USA refers to the separate, generally soft and fluffy, cushion used to place under the head while sleeping, In other countries very hard pillows may be used for this purpose.


A term used in rigid foam spraying to refer to the sagging of the foaming mixture that sometimes occurs during spraying of a vertical surface. Among the many causes of this are slow gelation, excessive buildup, lack of proper temperature control of the chemical components or the target surface, etc.


See haze.

Solid Elastomer

A term used to refer to rubber like compounds that have no internal cavities or gas bubbles.

Solid Filler

An insoluble Additive to a urethane foam formulation that remains a finely divided solid even after blending into the mixture. It is often used to add weight to a formula while reducing the formula cost, to add firmness to the foam or greater viscosity to the liquid mixture. Generally tensile strength is reduced by this type filler.


A substance, usually liquid, used to dissolve another substance.

Solvent Blown Foam

See blowing agent. Many different types of low boiling chemicals have been used as blowing agents in urethane foam, most of them normally classed as solvents.

Solvent Flush

A term which refers either to the rinsing of the mixing chamber with a solvent or to the equipment required. This can be accomplished by many methods ranging from a plastic squeeze bottle, through manual valving to completely automatic types. In some cases an air flush or purge follows the solvent flush to ensure that no solvent remains in the mixing chamber when the next mix cycle is initiated. Methylene chloride is the most commonly used cleaning solvent.

Solvent Flush Cycle

A term used to describe a solvent flush, air flush cycle (or solvent cycle only), and indicates the time of each. For example, a typical solvent flush cycle might be 5 seconds of solvent followed by 10 seconds of air. The cycle may be initiated by push button and controlled by timers so that it automatically shuts off and resets for the next push button actuated cycle; it may be automatically initiated by timers or manually initiated by opening a valve. The timers are normally adjustable so that more or less air or solvent can be forced through the mixing chamber as required.

Solvent Flush Timers

Timers used to control the quantities of solvent and air dispensed during a solvent flush cycle by controlling the duration of the 'on' cycle of a valving device or pumping mechanism.

Solvent Resistance (Solvent Swell)

A term which refers to the durability of material exposed to solvent. It is usually measured by determining the percentage weight increase after a specified number of hours of immersion in the solvent. A 10 to 15% increase in weight is usually not too objectionable.


See flashing.

Specific Gravity

The density of any material divided by that of water at a standard temperature, usually 4' C. Since water’s density is nearly 1.00 g./cc., density in g./cc. and specific gravity are numerically nearly equal.


A splattering which sometimes occurs when the mixed liquid is poured into a mold or onto a conveyor. The spattering or splashing may cause the formation of large bubbles which can be trapped in the rising foam, showing up as large cavities or voids in the foam during cutting.



A rather ambiguous term used to describe many different foam products. It is most often used to describe 'Blown Elastomers', particularly those with high load bearing and higher densities (8 pounds per cubic foot and higher). It sometimes is used to refer to an open celled product, and sometimes to a completely closed cell product.

Spray Mixing Head

A mixing head in which the primary cause of mixing is the atomization and turbulence created in the mixing zone by one or more high velocity air jets. Mixing may be external to the nozzle and completely dependent on the air turbulence for mixing, or internal and partially dependent on impingement onto the interior walls of the mixing chamber. See external mix.


A device to assist in placing a uniformly distributed layer of mixed foam components into a mold or onto a conveyor prior to foaming in an effort to minimize flow of the expanding mass during foaming. A typical device of this type consists of a horizontal track supported at each end on which a moving carriage rides. The mixing head is mounted on the carriage, and the carriage is driven back and forth by a drive mechanism. The drive mechanism can be linear or rotary pneumatic, hydraulic, mechanical or electrical.


A term normally used to refer to those Additives that assist in maintaining the quality of the foam in use such as anti-oxidants, ultraviolet absorbers, acid absorbers, etc. Occasionally it is used to refer to foam stabilizing Additives such as the silicone compounds that add stability to the semi liquid expanding mass. stannous octoate-one of the more commonly used organotin catalysts, particularly for flexible one shot foam. One of the major reasons for its preferential use is that it is usually destroyed or converted to a less active form by the exothermic heat of the reaction, minimizing degradation in the final foam product.

Stannous Oleate

An organotin catalyst of the stannous octoate type. It is approximately 1/2 as active, by weight.

Static Fatigue

A term which describes the loss in load-bearing properties of a foam sample under constant compression.

Stator Blade

A term sometimes used to refer to non-rotating or non-moving baffles that assist in mixing foam components by forcing the liquids to follow a labyrinth like path through the mixing chamber. See labyrinth mixing and helical spiral mixing.

Steel Rule Die

A device used for stamping pr 'clicking' out intricate or simple shapes from sheets of foam or other soft material. They are manufactured by imbedding narrow bands of sharp edged steel into a wooden back plate in the pattern desired. The sharp edge of the die is placed against the surface to be cut; the die is then hit a sharp blow with a mallet or with the platen of a 'clicking' press which drives the die through the material and cuts out the desired pattern. See 'clicking'.

Step Throughput

The practice of interconnecting drive motors and pumps with a multi path gear box so that several different 'fixed or 'step' outputs or throughputs are available rather than the more usual infinite variation between fixed upper and lower limits.


A term which refers to the relationship of the various combining weights of several interacting chemicals. For example, it takes approximately 10 grams of TDI to completely react with 100 grams of standard flexible foam type polyol and approximately 1 gram of water to completely react with 10 grams of TDI. A stoichiometrical balance is achieved when 100% of all the chemicals used in the reaction are consumed in the reaction. In the urethane industry this stoichiometric balance is termed 'having an index of 100.' See index.

Straight Sided Impellers

Mixing blades or impellers that have parallel sides or cylindrical shape as opposed to tapered sides or cone shape.


A term which sometimes is used to describe the flow of liquid of one of the components in the formula or the circuit through which it flows. For example, the flow of TDI from the nozzle during metering may be called the 'TDI stream'. Also in slab foam terminology 'upstream' would be 'against' the flow of foam, and 'downstream' would be 'with' the flow of foam.


Lines and/or streaks of cream colored liquid extending upstream from the cream line into the clear liquid dispensed from the mixer during the slab foam process. They may be from 0 to 24 inches or more in length but are generally kept between 2 and 6 inches long by careful regulation of the angle of rise, the conveyor speed, the flow rate, the catalyst quantity or balance, etc. Streamers are an important guide to quality control, and if all variables are properly controlled, will always appear the exact same distance downstream from the mixing head with the same formula . Different formulas may have different distances. Excessively long streamers will generally forecast the presence of splits; excessively short or non existent streamers will forecast undercutting and the presence of flow lines and/or side and top cracking.

Stress Relaxation

Due to the viscoelastic nature of plastics, the amount of force or stress necessary to produce a given amount of deformation gradually decreases during the time the stress is applied. This decay of stress at a constant deformation is called stress relaxation.


See flow lines.

String Time

With rigid foams the time between pouring the mixed liquids into the container and the time that long 'strings' of tacky material can be pulled away from the surface of the foam when the surface is touched with a wooden spatula or even with the fingers.


A term generally used with spray foam Applications to describe the surface on which the foam is applied.

Super Foot

A European term usually synonymous with the American 'board foot' which is 12 inches x 12 inches x 1 inch. This measurement of volume is used as a convenient frame of reference for pricing both rigid and flexible foam stock (cut slab foam).

Surface Active Agent

An Additive to the formulation that either helps or hinders the formation of a fine, uniform cell structure in the resultant foam.

Surface To Volume Ratio

A means of differentiating between cavities with the same volume but vastly different shapes. For example, a cube with a volume of 1 cubic foot would have a surface area of less than 1000 square inches. The same volume, distributed so that the cavity was only 1inch thick. would have a surface area of over 3000 square inches. The two different shapes of cavities require different techniques and formulations in order to exactly fill them with equal amounts of foam.


A commonly used contracted or shortened form of ' surface active agent'. See silicones.


The momentary increase in relative flow rate that occurs in a fluid metering system when the pressure drops from a previously higher but stable level to a lower and again stable level. With 'on-off' mixing heads, this can occur at the instant of diversion of flow from recycle to mix if the operating pressures under both conditions have not previously been balanced. Theoretically the surge would not be of significant quantity if the metering system had no flexible hoses or places in which air or gas could be trapped, but unfortunately it is usually necessary to carefully balance the pressure to avoid off ratio foam spots in the product.

Swivel Adapter

A special hose to pipe fitting or adapter that is so constructed that one permanently attached end freely rotates, permitting easy assembly and disassembly of parts. Occasionally swivel adapter and fitting are used interchangeably. See swivel fitting.

Swivel Fitting

A special hose or pipe fitting that is so constructed that one permanently attached end freely rotates, permitting easy assembly and disassembly of parts. See swivel adapter.

Synergism (Synergistic)

The property exhibited by a blend of some materials, having a greater effectiveness or chemical activity as a mixture than would ordinarily be expected from the sum of their independent abilities or activity levels. Some combinations of urethane foam catalysts would appear to have this property.


A rather ambiguous term used to describe almost any combination of mechanical parts or chemicals that have some relationship to each other. For example, the metering mechanism is often described as the 'metering system' which includes just the mechanical parts. A 'froth system', on the other hand, usually includes the chemicals within its scope and might even refer to the chemicals by themselves. A 'complete system' is sometimes used interchangeably with 'complete package' to indicate everything needed. to produce foam (machine, chemicals, process know how, etc.).


A common symbol for tolylene diisocyanate, particularly the 80-20 isomer blend although it is sometimes used for other blends, Occasionally it is misused to represent any isocyanate bearing material, resulting in some confusion since many of the so-called 'crude or undistilled isocyanates' are not related to TDI at all other than by the attached NCO groups.


Is a symbol for one of the Amine catalysts used in foam formulations. The actual name of the catalyst is N,N,N1,N1- tetramethyl-l,3-butanediamine making it easy to understand why the symbol is used.


A symbol for one of the Amine catalysts used in foam formulations. The actual name of the catalyst is N,N,N1,N1- tetramethyl ethylenediamine.


A symbol for one of the Amine catalysts used in foam formulations, particularly rigid foam. The actual name of the catalyst is tetramethyl guanidine.


A device used to indicate the speed of some mechanism, usually the number of revolutions per minute of a pump or impellers. Under specified operating conditions, tachometer readings can be accurately related to flow rate. The combined information from tachometers, temperature gauges, pressure gauges, metering data, etc., provides the necessary background on which to base troubleshooting judgments. tachometer indicator-the dial or meter portion of a tachometer device that actually displays the information.

Tack-Free Time

The time between pouring the liquid mixture and the time that the surface of the foam can be touched with a spatula or a finger without sticking. This is a very difficult interval to relate positively to other factors since it is often influenced by environmental temperature and humidity. See also string time and rise time.

Tacky Surface

The condition of the surface of a foamed object, particularly free rise in the atmosphere, during which any object touching its surface will stick to the surface. This is normally a stage in the cure through which foams pass on their way to final cure. See tack-free time and string time.

Take-Away Conveyor

A name given to a conveyor on the discharge side of an in-line cutoff saw that is designed to take away the cut pieces of foam at a slightly faster rate than that of the main foam conveyor in order to prevent fouling the saw blade.

Tapered Impeller

A mixing blade or impellers characterized as having nonparallel sides coming closer together towards the discharge opening. Symmetrical impellers of this type could be called cone shaped with the inlet being the wide end of the cone and the outlet being at the narrow part of the cone. See straight sided impellers.

Tear Resistance

The ability of a piece of flexible foam to resist deepening a cut already made in the foam sample.


The special technical language often used by science or engineering trained personnel which has meaning only to others of similar training.

Temperature Conditioning

The process of bringing the object or surface to a specified operating temperature. It is normally used to indicate a passive operation such as storing drums of chemicals in a room with a controlled temperature between 70° and 75° F., allowing the chemicals to acquire the temperature of the room over a several day period, with no attempt at agitation of the drum contents. Foam samples prior to testing are temperature conditioned.

Temperature Indicator

That portion of a temperature sensing device that displays the information on a dial or meter.

Temperature Indicator-Controller

A combination of temperature sensing element, temperature display and thermostat. This is used for controlling the temperature of one of the urethane foam components in a metering system through control of the operation of a heat exchanger.

Temperature Stratification

The unmixed or layered condition often encountered in machine tanks without agitation, particularly the larger ones. Under some conditions warmer material returning to the tanks after passage through a heat exchanger will slide out on top of the cooler material without mixing, resulting in a warm strata at the top and a cold strata at the bottom. Under other conditions the warmer material will channel right through to the pump suction, leaving the bulk of the colder material in the tank and out of the flow circuit. tensile strength-normally expressed as the pounds per square inch of force required to stretch a foam sample to the breaking point. See elongation.

Tertiary Amine

An Amine catalyst of the type useful in urethane foam reactions, characterized by a molecular structure in which the nitrogen is directly connected to organic radicals only and not to hydrogen atoms as in ammonia. The tertiary Amines are generally more powerful catalysts than the primary or secondary types of Amines.

Testing Equipment

The equipment or devices necessary to carry out the Test Methods. It should be kept in mind that although some degree of testing is necessary for quality control, most of the tests necessary cannot be performed with any degree of Accuracy within two or three days of the production run of foam. In most cases this foam would already be distributed to the customers so that for practical purposes quality control starts with the foam production equipment and is directly dependent on it. Many manufacturers have so called 'quick tests' which they use to exAmine the uncured foam. These are relative rather than absolute but can be quite useful.

Thermal Conductivity

Ability of a material to conduct heat; physical constant for quantity of heat that passes through unit cube of a substance in unit of time when difference in temperature of two faces is 1 degree.

Thermal Froth

The production of a partially expanded fluid from the discharge nozzle of the mixer by means of heating the component(s) containing fluorocarbon 11 to levels far above the normal boiling point, while maintaining them under pressure from the tank through the mixing zone. The sudden reduction of pressure at the discharge nozzle allows the blowing agent to boil, and thus partially expand (or froth) the discharging liquid mixture. This is apparently a useful technique for working with high viscosity or high elastic component polyols that are otherwise difficult to keep mixed after discharge and prior to the cream time.

Thermal Gravimetric Analysis

The analysis of a foam sample by graphically recording the weight loss of the sample at different temperatures through the decomposition point or zone. See differential thermal analysis.


A material which is capable of softening or melting at elevated temperatures without degradation so that cooling of the material restores it to its original condition.


A material that is cured or transformed by elevated temperatures into a solid condition from which it does not change, upon reheating, until it reaches the decomposition point. Most urethane materials are thermosetting materials (e.g. flexible and rigid foams). Certain urethane elastomers and fibers are thermoplastic.


Refers to the ability of a fluid to be jelly-like or semi-solid at rest, but reverting to a liquid on being agitated or stirred. Some degree of thixotropy helps a spray formulation to achieve greater thickness in a single pass.

Three Roll Paper Feed System

A system of paper supply for a slab foam conveyor consisting of a single bottom sheet of paper with two separate side sheets. The three roll type is usually tied in with a paper unrolling or removal system of the constant tensioning type. Although this system is more expensive than the single roll type, it usually pays for itself through fewer wrinkles and less foam damage. In addition there is greater freedom of paper supply when producing extremely wide Blocks of foam, since paper roll widths required are up to 4 or 6 feet less than that required for a single roll system. See paper handling device.


A synonym for flow rate.

Throughput Control

The condition of being able to vary the flow rate or throughput of a metering machine.

Throughput Indicater

Any one of several devices that have been calibrated to have some direct relationship with flow rate such as tachometers, speed adjusting knobs, flowmeters, etc.

Throughput Rating

A term which applied to metering machines and mixing heads generally refers to the maximum flow rate that can be metered and mixed with all pumps at their maximum delivery or with some specified formulation. This can be a very misleading statement because of the diversity of formulation ratios for urethane foam. For example, a machine with maximum flow rate of 30 pounds per minute with a 50-50 ratio for a 2 component formula may only be able to deliver 15 to 16 pounds per minute of a total prepolymer formula with a 97/3 ratio. Under some conditions of extreme high viscosity the maximum flow rate may not be achieved within the pressure or pump suction limitations of the machine.

Throw Pillows

Tin Catalyst


A specified allowance for deviations in weighing, measuring, etc., or for deviations from the standard dimensions or weight. Also applied to foam formulations. A formula is said to have tolerance if it can reproduce good quality product from day to day despite variations in raw materials, environmental conditions or small metering errors.

Tombstone Effect

A term used to describe a weakness that can occur in the joint area between multiple pours of foam in a single, usually thin, high rise cavity. The name comes from the characteristic shape of the joint shown in a vertical cross-section of the foam. Under certain conditions severe cracking can occur in this area during exposure to -15° F. temperatures.

Top Cracks

Cracks in the top surface of a foam slab that extend across the width of the conveyor. The edges of the cracks are widely separated and the inner surface of the crack is fairly smooth because they occur during a liquid phase. This is usually associated with undercutting. In contrast the edges of a split are usually close together and the inner surface is rough or jagged because they usually occur later during the final stages of polymerization.

Top Cure

The process of shortening the tack-free time of the top skin of continuous slab foam by heating it with radiant, steam or hot water heat. It is highly desirable that all tack (or tackiness) should be gone by the time the slab foam is cut, handled and stacked.

Top Cure Oven

The oven or device used to effect top curing of foam slab.

Top Splits

See flaps.

Topper Pads

Thin cushioning pads used as the top layer of an automobile seat to provide a good 'feel' to the seat.

Total Flow Rate

See flow rate.

Total Prepolymer

A urethane foam intermediate in which all of the isocyanate material is premixed with all of the polyol material and reacted under controlled conditions. To make foam this prepolymer is then blended with a catalyst mixture consisting of the water, catalyst and surfactant. The ratio between the total prepolymer and the catalyst mixture is about 97/3 or 95/5. See also prepolymer, modified total prepolymer, partial prepolymer and one shot.

Transfer Pumping

A term which generally refers to the method of filling the foam machine tanks or of keeping them filled. The most usual technique is to use air operated bung pumps installed in the chemical supply drums. These can be either manually valved at the machine tank or connected in conjunction with a level control device which automatically causes shut off of the transfer pump at the proper time. The term also is used to refer to the elaborate pumping network installed in the factories of large foam producers who buy their chemicals in bulk. The purpose of the network is to transfer the bulk chemicals to the proper machine tanks at the proper time.


Another ambiguous term referring to movable equipment. See portable and movable.

Traveling Cut-Off Saw

Traverse Mechanism

See spreader.

Triethylenedi Amine

The chemical name of one of the more common Amine type catalyst used to make urethane foam. It is one of the most active.


A term which refers to the small pieces of good quality foam that are removed from the crude Block of foam during converting operations. Trim consists of bottom, top, and side skins plus odd length or thickness leftovers. With proper management many profitable items can be manufactured from this trim material. See also scrap and crumb.

Trim Loss

The percentage of the total good foam produced that is not sold directly after the primary cutting operation but must be further cut or converted or reduced in price in order to be saleable. The percentage may be by weight or by volume. Trim losses as low as 3% and as high as 45% have been reported.


A polyol characterized by having three reactive hydroxyl (OH) groups attached to the molecule.

Two Phase Material

A term which generally refers to a composite material such as a fiber or pellet filled plastic or foam in which the composite has superior properties to either of the starting materials.

'U' Value

The overall coefficient of heat transfer. This value incorporates all the factors involved in the transfer of heat from one area to another, including boundary layer transfer and any or all 'IC' factors. 'U' values are generally used in calculating heat transfer of a structure in a particular environment; whereas 'IC' factors are generally used for single components of a structure.

UV Stabilizer (Ultraviolet)

Any chemical compound which, when admixed with a resin, selectively absorbs UV rays. ultraviolet-zone of invisible radiations beyond the violet end of the spectrum of visible radiations. Since UV wavelengths are shorter than the visible, their photons have more energy, enough to initiate some chemical reactions and to degrade most plastics.


A term used in foam slab work, particularly flexible foam, to describe the appearance of the foam front when the angle of rise is so great that the streamers have disappeared underneath the rising foam. This can result in flow lines, side and/or top cracking and the entrapment of large bubbles in the center of the foam slab.


A term used in pour-in-place work to describe the condition of not having completely filled the void or mold with foam. Either not enough chemicals were used, or the foam failed to expand the expected amount.

Undistilled Poly Isocyanate

A term used by some companies in place of 'crude' or 'polymeric' isocyanate.


A term for years used as the common name for a chemical more properly called ethyl carbamate (a biological poison); the term is now used to refer to the product of a reaction between a chemical containing reactive isocyanate groups on its molecule and a chemical containing reactive hydroxyl groups on its molecule. These compounds are, for the most part, biologically inert. The compounds are called polyurethanes. Since the name refers to the molecular joint between the monomer, many different chemicals can be used as the building Blocks or 'monomers' with the final product still being known as a urethane compound or polymer.

Valve Block

That portion of the mixing head that is responsible for diverting the various flows simultaneously between recirculate and operate. These may be very simple, manually operated individual valves or more complex automatic devices that may divert from 2 to 6 components simultaneously.

Variable Calibration Time

The practice of catching in individual cups the output of all fluid streams simultaneously for an indefinite time period in order to check the ratio between fluid streams, but not the flow rate per minute.

Variable Flow Rate (Throughput) Control

The ability to be able to change the flow rate of any or all components as desired, usually within a fixed minimum and maximum limitation. See fixed flow rate.

Velocity Balance

A lead-lag problem, under some conditions of metering and mixing machine operation, in which pressures are exactly balanced (see pressure balance). This can be caused by unequal velocities of the components , perhaps due to extreme differences in viscosity or quantity. Under these conditions one material will reach the mixing-pumping zone before the other and will be expelled from the mixing chamber before enough of the other component has been blended in to bring the mixture back on ratio. This problem is more likely to occur with extreme differences in viscosity between the various components and can often be corrected by changing the diameter, length or direction of discharge of the metering ports as required.

Vertical Cutting Saws

Special foam cutting bandsaws in which the portion of the blade that is used for cutting is in the vertical plane. This type of saw is usually characterized by large moving tables that carry the foam Blocks past the cutting blade.

Vertical Pour

A term which generally refers to those pour-in-place operations in which the cavity to be filled is extremely long in its vertical dimension (height) in comparison to its thickness and generally is higher (vertically) than its width (horizontally). This would give the cavity a large 'surface to volume ratio'. This is also called a high-rise Application.

Vibration Eliminator

A term sometimes used to describe a special fitting on the suction side of a rotary pump that is used to isolate the pump from the tank by means of a rubber coupling or bushing so that stresses on the pump casing are reduced. This is particularly important when the pump is mounted directly beneath the tank.

Virgin Foam

A term often used to describe foam, particularly flexible slab foam, that has not been processed in any manner other than cutting to shape. It is a means of differentiating between rebonded, laminated or pieced together foam and the original or 'virgin' material.

Viscoelastic Behavior

A term which generally refers to the flow characteristics of a material which is not completely rubber- like, not really rigid and not readily fluid.


The resistance of a fluid to being fluid (or flowing readily). For example, a low viscosity material would flow readily from a container on being poured, while a high viscosity material would only pour slowly from a tipped container. See centipoise and poise.

Viscosity Range

The scope of viscosities, between stated maximum and minimum limits, that can be handled properly by a metering machine, pumping system, pump, mixing head or other specified item. Usually viscosity range is coupled with flow rate range and under some conditions can cause confusion, since a particular machine may not be able to achieve maximum flow rate with maximum viscosity material or may not be able to achieve stated Accuracy of flow at the minimum flow rate with the minimum viscosity material.


A term generally used to describe any fluid more resistant to flow than water. The degree of viscousness (viscosity) is generally expressed in centipoises in the foam industry. For clarification, see poise or centipoise.

Void Filling

A term occasionally used as a synonym for pour-in- place. When used it generally refers to filling structural cavities rather than the filling of molds.

Water Absorption

A term used with rigid foam to describe the percent by weight of water pickup on submergence of a specified sample under a specified depth of water.

Water Blown Foam

Foam in which the gas for expansion was generated by the reaction between water and an isocyanate bearing material. See blowing agent for further clarification.

Water Vapor Permeability

(WVP)The rate of transfer of water vapor through a film of the polymer. This is normally determined by an indirect test method on cast films of the solid polymer rather than on the foam itself. This is sometimes called water vapor transmission (WVT).


An instrument which is utilized to subject articles to accelerated weathering conditions, e.g., rich UV source and water spray.


A term sometimes used to describe scattered large bubbles that occasionally appear in large Blocks of slab foam that are otherwise uniform in cell structure.


Cell membranes or walls in flexible foam that are unbroken or ruptured but intact, which interfere with free air movement through the foam structure. Generally a high proportion of windows, as indicated by the shiny or glittering reflection of light from a cut surface, indicates a foam tending towards closed cells and consequently possibly rather poor in some physical properties. Usually a reduction in the organotin catalyst level in relation to the Amine catalyst level will reduce the incidence of windows. There are other processing factors which can also affect their presence.

Worm Holes

See rat holes.

Yield Point

See elastic limit. This is the point in compression or tension loading of a sample beyond which permanent damage to the structure of the sample results. Before this point complete elastic recovery will occur. Commonly rigid foam is defined as that foam having a yield point of less than 10% (compression or elongation).

Yield Strength

The force required to bring a specified sample of foam to the yield point. The force is usually stated in pounds per square inch.

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