By Maura Keller
Density is the weight per unit volume of the foam normally expressed in kilograms per cubic meter (kg/m3). The general range of polyether flexible polyurethane foams is 16 to 64 kg/m3. This density is not a measure of firmness as it is with latex rubber foams. Density is an important factor, however, in that for a given load-bearing requirement, a higher density foam generally gives better quality and performance. The denser the foam, the heavier the foam.
ILD (Indentation Load Deflection) is an indication of the load-bearing ability of a foam. The standard test is to depress a 50-square-inch indenter plate into the foam and measure the number of pounds required to achieve a desired deflection. The firmer the foam, the more force (in pounds) needed for the deflection and hence the higher the ILD number (in pounds). This is described in ASTM Test Method D-1564 and is no longer used as a description of load bearing.
CFD (Compression Force Deflection) is a measure of the load-bearing ability of a foam. It is the force exerted against a flat compression foot larger than the specimen to be tested. The value can be expressed at 25-, 40-, 50- and/or 65-percent compression.