Facts About Foam: Definitions
Density
is the measurement
of the mass per unit volume. It is normally
recorded in pounds per cubic foot (or kilograms
per cubic meter (kg/m3)), and is simply the
sample weight divided by its volume. In foam,
density is an indication of quality and lasting
comfort. The denser the foam, the more resilient
it will be. Thus, density is equivalent to
performance durability. In addition, the higher
the density, the higher the cost. (Density and
compression are not related.)
Identification Force Deflection (IFD) is a measure of the load bearing capacity. IFD is generally measured as the force (in pounds) required to compress a 50 square inch circular indentor foot into a four inch thick sample (typically 15 inches square or larger, to a stated percentage of the sample's initial height). Common IFD values are generated at 25 and 65 percent of initial height.
Compression is basically equivalent to 'firmness'. It is measured by a number called the Indentation Load Deflection (ILD) or the Indentation Force Deflection (IFD). These tests measure the pounds of force it takes to compress foam. The higher the IFD number, the firmer the foam. Firmness is controlled by the way the foam ingredients are mixed, whereas density is determined by the total amount of foam ingredients. You can have both soft and firm foams at the same density. (Density and compression are not related.)
Elongation indicates the extent to which foam can be stretched before snapping apart. An elongation of 200% means that a strip of foam 4 inches long can be stretched to 12 inches before breaking.
Flex Fatigue (Dynamic Fatigue) is a softening or loss of firmness. Flex fatigue is measured in the laboratory by repeatedly compressing a foam sample and measuring the change in IFD. Several different protocols, including methods contained in ASTM, ISO, and BIFMA testing standards, may be used. Even ASTM 3574, one of the more widely used sets of testing standards, contains multiple testing methods. In selecting one or more test methods, it is important to consider the intended foam application and to choose a testing protocol that closely simulates the intended application.
Tensile Strength (Tear Strength) is a measure of the force required to continue a tear in a foam after a split or break has been started and expressed in pounds per inch (lb./in.). This property is important in determining the suitability of foam in applications where the material is sewed, stapled, or otherwise anchored to a solid substance.
Resilience is an indicator of the surface elasticity or "springiness" of foam. The resiliency test determines the spring the foam has, surface liveliness and spring-back ability. A foam with a high resiliency will have greater spring-back. Resiliency is measured in a lab with a Ball Rebound test. A steel ball is dropped onto the foam sample from a fixed height. It is expressed as a percentage of ball rebound against the original height of the ball drop. A boardy (an undesirable stiff surface feel) foam will have low resilience.
Hysteresis is the measurement of a foam's ability to maintain original support characteristics after flexing. Normally, the firmness (IFD) is tested at 25% indentation, 65% indentation and again at 25% on the way up. Hysteresis is the percent of 25% IFD loss measure as a compression tester returns to the normal (25% IFD) position after measuring 65% compression. Lower hysteresis values, or less IFD loss are desirable. Current research indicates that hysteresis values may provide a good indication of overall flexible foam durability. Low hysteresis in conventional foam is equal to less IFD loss in durability and fatigue tests.
Flame Retardant is an additive which improves the base materials ability to resist combustion.
Static Fatigue indicates the relative degree of "foam softening" that can be expected during an active service life. The static fatigue test developed to forecast this relative softening involves compressing the whole foam sample by 75% for 22 hours at room temperature and noting the loss in load-bearing capacity (25%) after the test.
Identification Force Deflection (IFD) is a measure of the load bearing capacity. IFD is generally measured as the force (in pounds) required to compress a 50 square inch circular indentor foot into a four inch thick sample (typically 15 inches square or larger, to a stated percentage of the sample's initial height). Common IFD values are generated at 25 and 65 percent of initial height.
Compression is basically equivalent to 'firmness'. It is measured by a number called the Indentation Load Deflection (ILD) or the Indentation Force Deflection (IFD). These tests measure the pounds of force it takes to compress foam. The higher the IFD number, the firmer the foam. Firmness is controlled by the way the foam ingredients are mixed, whereas density is determined by the total amount of foam ingredients. You can have both soft and firm foams at the same density. (Density and compression are not related.)
Elongation indicates the extent to which foam can be stretched before snapping apart. An elongation of 200% means that a strip of foam 4 inches long can be stretched to 12 inches before breaking.
Flex Fatigue (Dynamic Fatigue) is a softening or loss of firmness. Flex fatigue is measured in the laboratory by repeatedly compressing a foam sample and measuring the change in IFD. Several different protocols, including methods contained in ASTM, ISO, and BIFMA testing standards, may be used. Even ASTM 3574, one of the more widely used sets of testing standards, contains multiple testing methods. In selecting one or more test methods, it is important to consider the intended foam application and to choose a testing protocol that closely simulates the intended application.
Tensile Strength (Tear Strength) is a measure of the force required to continue a tear in a foam after a split or break has been started and expressed in pounds per inch (lb./in.). This property is important in determining the suitability of foam in applications where the material is sewed, stapled, or otherwise anchored to a solid substance.
Resilience is an indicator of the surface elasticity or "springiness" of foam. The resiliency test determines the spring the foam has, surface liveliness and spring-back ability. A foam with a high resiliency will have greater spring-back. Resiliency is measured in a lab with a Ball Rebound test. A steel ball is dropped onto the foam sample from a fixed height. It is expressed as a percentage of ball rebound against the original height of the ball drop. A boardy (an undesirable stiff surface feel) foam will have low resilience.
Hysteresis is the measurement of a foam's ability to maintain original support characteristics after flexing. Normally, the firmness (IFD) is tested at 25% indentation, 65% indentation and again at 25% on the way up. Hysteresis is the percent of 25% IFD loss measure as a compression tester returns to the normal (25% IFD) position after measuring 65% compression. Lower hysteresis values, or less IFD loss are desirable. Current research indicates that hysteresis values may provide a good indication of overall flexible foam durability. Low hysteresis in conventional foam is equal to less IFD loss in durability and fatigue tests.
Flame Retardant is an additive which improves the base materials ability to resist combustion.
Static Fatigue indicates the relative degree of "foam softening" that can be expected during an active service life. The static fatigue test developed to forecast this relative softening involves compressing the whole foam sample by 75% for 22 hours at room temperature and noting the loss in load-bearing capacity (25%) after the test.