Indentation Load Deflection (ILD) is a measurement of foam firmness. Firmness is independent of foam density, although it is often thought that higher density foams are firmer. It is possible to have high density foams that are soft â€“ or low density foams that are firm, depending on the ILD specification. ILD specification relates to comfort. It is a measurement of the surface feel of the foam. ILD is measured by indenting (compressing) a foam sample 25 percent of its original height. The amount of force (in pounds) required to indent the foam is its 25 percent ILD measurement. The more force required, the firmer the foam. Flexible foam ILD measurements range from 10 pounds (supersoft) to about 80 pounds (very firm).