Foam Glossary

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Air Flow
Amount of air expressed in cubic feet per minute, that can be drawn through a 2" x 2" x 1" FPF sample at .5-inch water pressure differential.

American Society for Testing and Materials. An organization devoted to the establishment of standard methods and procedures for testing materials.


Ball Rebound
A test procedure (ASTM D3574) used to measure the surface resilience of FPF. The test involves dropping a standard steel ball on known mass from a predetermined height onto a FPF sample and measuring the percent of rebound.

Barrier Material
A barrier placed between a cover fabric and filling materials to slow heat transfer and flame spread to the filling material.

A cut-off segment of the continuously produced flexible polyurethane foam being made by the slabstock 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 skins may be removed by in-line trimmers, leaving a smooth rectangular block.

Board Foot
Unit of measurement in the flexible polyurethane foam industry equal to a square foot of material one inch in thickness.

FPF with a stiff or rigid feel, generally indicated by high 25% IFD values and low compression modulus.

A loose pillow, flexible polyurethane foam and/or fiber filled, that is not attached to the upholstery frame.

Bonded FPF
FPF particles or shredded FPF (often manufacturing scrap) that has been glued to form a useful product. The resultant FPF block is peeled into the desired thickness. Largest use is for carpet cushion.

The combination of two r more components into a multiple-layer composite. In furniture applications, FPF is often adhered to other FPF grades or to polyester fiber.

Boston Chair Test
Boston Fire Department test method to measure performance of FPF padding materials when exposed to a fairly severe flaming ignition source. This test is a full scale composite test. Test method is now similar to California TB 133 with additions.

Bottom Out
The lack of support by a flexible polyurethane foam under full load. This term is very subjective, as a foam may bottom out with a heavy person, and be very comfortable to a lighter-weight individual.

See Air Flow.

See Blocks. Generally, buns are longer than blocks, approximately equal to or greater than 60 feet in length.

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California Technical Bulletin 117 FPF
FPF that will meet the component combustibility requirements of this standard.

The cavity remaining in the structure of flexible polyurethane foam surrounded by polymer membranes or the polymer skeleton after blowing is complete.

Cell Count
The number of cells per linear inch or centimeter, expressed as pores per inch or pores per centimeter.

Cell Size
The average diameter of the cells in the final flexible polyurethane foam product, often measured in micron units.

Cell Opening
In FPF materials, the breaking of membranes within the sell structure, permitting flow of air through the material.

FPFs that have been made without the use of chlorofluorocarbons as auxiliary blowing agents.

Compression Force Deflection (CFD)
The determination of the resistance to compression of a flexible polyurethane foam sample when the entire surface area of the sample is compressed. Test method is described in ASTM D3574.

Closed Cells
FPF cells having intact cell membranes thereby reducing or eliminating passageways for airflow. Used for winter snow camping, etc.

Cold-Cure Foam
See high resiliency foam

The ability of the cushioning structure to deflect at the surface and to conform to body shape, preventing a concentration of pressure on the body.

Compression Modulus
Ratio of an FPF's ability to support force at different indentation (or compression) levels. It is determined by taking the ratio of the FPF's IFD at 25% indentation and 65% indentation (65% IFD/25% IFD). The compression modulus is typically a function of FPF chemical formulation and the manufacturing process. In most cases, the higher the density the greater the compression modulus. Other terms that are used interchangeably are: support factor, and modulus.

Compression Set
A permanent partial loss of initial height of a flexible polyurethane foam sample compression due to a bending or collapse of the cell lattice structure within the foam sample. Large percentages of compression set will cause a flexible polyurethane foam cushion to quickly lose its original appearance with use, leaving its surface depressed or "hollowed out".

Constant Deflection Compression Set
Test used to determine the amount of foam recovery from a static or fixed compression. Test method is described in ASTM D3574.

Conventional FPF
Polyether type FPFs made by the basic manufacturing process.

An FPF product resulting from a fabrication process involving the use of special cutting equipment to produce an FPF sheet with peaks and valleys. [Egg-crate foam]. This texture gives the foam a different surface feel, or apparent softness.

The ability of the cushion system to distribute body weight uniformly over the seating area.

A conditioning process using a mechanical or vacuum-assisted procedure to open the closed cells of a high resilience slabstock or molded FPF.

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To compress, usually by a specified amount or percentage.

A measurement of the mass per unit volume. Foam density is often expressed as pounds per cubic foot or kilograms per cubic meter. (Test Method ASTM D3574). Density is usually measured in grams/cm3 and multiplied by 62.4 to convert to lbs/ft3 (pcf). Density is not a measure of firmness, stiffness, or load bearing capacity. That is defined by Indentation Force Deflection (IFD) or Compression Force Deflection (CFD). As density increases, FPF's cell walls become thicker and more durable. Thus, higher density foams last longer that lower density foams. For conventional FPFs, "low density" foams extend from 0.8 lbs/ft3 to 1.2 lbs/ft3. Medium density is 1.5 lbs/ft3. For more durable sofas, 1.8 lbs/ft3 ["high density"] FPF is specified for upholstery by quality manufacturers and furniture stores. More durable than conventional FPFs are high resilience ["HR"] FPFs.

A material that has been made more dense by permanently compressing a unit mass into a smaller volume.

Description of what occurs when a weight is placed on the center of a cushion and the corners of the cushion rise up in response.

How well an FPF retains its comfort, support and shape with use. Durability is linked to density: the higher the density, the higher the durability.

An instrument used to measure hardness of elastic materials. Durometer is also used to reference a scale of hardness; ie, a low durometer implies a soft material

Dynamic Fatigue
A durability test performed in the laboratory using roller-shear or pounding type mechanisms.


Environmentally Safe
Flexible polyurethane foam processed with no auxiliary blowing agents.


A tendency to soften under cyclic stresses. Fatigue of foam samples can be measured by cyclicly compressing and relaxing a FPF sample and measuring its change in IFD.

See Hand.

The new acronym used to describe flexible polyurethane foam.

Filled FPFs
FPFs that have inorganic materials, such as marble dust, barium sulfate, graded sand or clay added to the foam during polymerization to increase foam density. These inorganic fillers are not chemically bonded into the foam polymer. They are instead mechanically trapped within the molecular structure of the polymer. Substantial amounts of filler may increase the foam's support factor, but may be detrimental to resiliency, strength, or durability.

The inorganic materials added to foam to increase foam density.

Finger Nail
A quick, general test for boardiness or stiff surface feel FPF. A finger nail pressed into a foam sample that leaves a definite impression that does not quickly recover indicates a boardy foam.

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Flexible polyurethane foam that has adequate support under load and does not "bottom out" is said to have "guts".


Hand is the feel of the surface of FPF when rubbed lightly. Stiff or hard feel is poor hand. Good hand is described as a springy, velvet feel.

Hardness Index
Synonym for the 50% IFD value. Some furniture designs are for a maximum 50% indentation while some are for only a 20% indentation, ie., chairs versus bar stools.

High Comfort (HC) FPF
Low density (1.8 - 2.6 lbs/ft3 high resilience FPF.

High Resilience (HR) FPF
High Resilience FPF have a high support factor and greater surface resilience hat conventional FPFs and are defined in ASTM D3770. High resilience FPF has a less uniform (more random) cell structure, different from conventional products. The different cell structure helps add support, comfort, and resilience or bounce. High resiliency FPFs commonly start at 1.8 lbs/ft3 and extends through 2.6 lbs/ft3.

The ability of FPF to maintain original characteristics after flexing. Lower hysteresis values, or less IFD loss are desirable.


Indentation Force Deflection (IFD)
IFD is generally measured as the force (in pounds) required to compress a 8" diameter steel plate into a foam sample to a stated percentage of the sample's initial height. For example, a 4" thick sample of foam is compressed until it reaches 3" thick, and the pressure needed to compress it is measured. Very soft foams might read 15-25 lbs IFD and be used for the upper layers of luxurious couches and mattresses. 35 lb IFD foams are used for medium firm foam mattresses, and 45 lb IFD foams are used for very firm foam mattresses. Common IFD values are generated at 25 and 65 percent of initial height. Note: Previously called "ILD (Indentation Load Deflection)."


Latex Foam
Latex sap comes from the rubber tree, like maple syrup from the maple tree. Factories make latex foam in molds like waffles at home. The latex sap is emulsified, poured into large mattress-size molds, quickly cured and cooled, leaving characteristic finger hole indentions on both sides. While latex foam is three times denser that HR FPFs and much harder to lift, it has the same high durability.


Modulus of Compression (MOC)
See Support Factor.

Molded Foam
A cellular foam product having the shape of the mold cavity in which it was produced.

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Open Cell Structure
A permeable structure in FPF in which there is no barrier between cells, and gases or liquids can pass through the FPF. Most cell walls have been ruptured to varying extent. All FPF for mattresses and sofas have an open cell structure.


The rate at which a liquid or gas can penetrate into or through a flexible polyurethane foam. Usually associated with airflow, a measure of the openness of the foam.

Flexible polyurethane foam that has been glued together from two or more smaller pieces. Commonly seen in cushioning to create special shapes or use up small pieces produced during fabrication.

The presence of numerous small cavities within a material. See Air Flow.

Pounding Fatigue
Accelerated fatigue aging of flexible polyurethane foam by cyclicly compressing samples to a specified percentage of their original height and releasing for a specified number of repetitions.

The practice of compressing an FPF sample up to six times to a predetermined thickness before determining IFD.


The process of adhering flexible polyurethane foam crumbs or shredded foam back together again to make a salable product. Rebonded foam is often used for carpet padding.

The return to original dimension and properties of a flexible polyurethane foam sample after a deforming force is removed.

The ability of a surface to spring back to its original shape after being deformed and released. The resiliency of flexible polyurethane foam is measured using the ball rebound test.

The amount of return to original dimension and properties of an FPF sample after a deforming force is removed.

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Slab Stock
FPF made by the continuous pouring of mixed liquids onto a conveyor, creating a continuous loaf of foam.

Static Fatigue
The loss in load-bearing properties of an FPF sample after being under constant compression. "Supersoft" FPF - FPFs that have an IFD measurement with the 7 to 10 pound range with a softness comparable to the feel of fiber.

Support Factor (see Compression Modulus)
Support Factor is a ratio os 65% IFD.25% IFD. When the support factor is known, it can be used in conjunction with a known 25% IFD value to determine the 65% IFD value. Seating FPFs with low support factors are more likely to bottom out.

Surface Firmness
The number of pounds of force necessary to indent an FPF sample by 25% of its original height.


Tensile Strength
The pounds per square inch of force required to stretch a material to the breaking point. Reference ASTM D-3574


Underwriters Laboratories. An independent, non-profit organization testing for public safety. UL is chartered to establish, maintain, and operate laboratories for the examination and testing of devices, systems, and materials to determine their relation to hazards to life and property.


Water Blown Foam
Flexible polyurethane foam in which the gas for expansion is carbon dioxide generated by the reaction between water and an isocyanate material. All flexible polyurethane foam is waterblown, although auxiliary blowing agents are often used to obtain special physical properties.

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