ASTM D1056 specifies a large number of different procedures for testing flexible cellular materials. The tests include compression set, similar to ASTM D395, tear resistance, adhesion resistance, and tensile and elongation tests. For our purposes we will focus on the test for compression deflection resistance.
There are several types of class, grade, and type specifications for these materials. The type can be open or closed cell type foam. The class has to do with it oil and temperature resistance. Finally, the grade rating is determined by the compression deflection given in PSI at 25% deflection.
Unlike ASTM D3574, the sample for compression deflection testing for D1056 is much smaller.
Compression Platens with a spherically-seated joint are required to perform these indentation force deflection (IFD) tests. Flexible cellular materials are very sensitive to any changes in humidity or temperature, so care must be taken to condition and test the foam under stable atmospheric conditions.
Indentation Force Deflection at 25% deflection is the standard result and is given by the load seen at 25%. IFD is also commonly referred to as Indentation Load Deflection (ILD). A similar reading can be taken at 65% and the two IFD values (25% and 65%) can be divided into each other to reveal the "support factor" which is a dimensionless number usually between 1 and 3.