Also called Compression Modulus and sometimes Comfort Factor, support factor is the ratio of a foam’s 65% IFD to its 25% IFD; in other words, how much more force is required to compress the material deeply than to compress it initially.
It measures the material’s progressive resistance: how quickly it becomes firmer as compression increases. A higher support factor generally means the material can feel relatively comfortable at the surface while providing stronger resistance at greater depths, helping reduce the tendency to bottom out under heavier loads. Higher progressive resistance is often associated with higher-performing materials, but support factor alone is not a universal measure of quality; the appropriate value depends on the foam type, formulation, and intended use.
Although support factor is discussed far less often than ILD, it is an important part of understanding how a foam will actually feel and perform. ILD describes firmness at a particular compression depth; support factor describes how that firmness changes as the material is compressed more deeply. Both are important when evaluating comfort and support.
