What is the IFD?
Indentation Force Deflection (IFD) tests measure firmness of flexible polyurethane foam cushions. High IFD test results imply increased hardness. Low IFD results indicate soft foam products. Note that the term IFD, or indentation force deflection, is interchangeable with ILD, or indentation load deflection. FIRMNESS. Firmness is an indicator of the surface feel of the foam. It is measured using the force in pounds required to indent a foam sample by 25% of its original height. This measurement is called Indentation Force Deflection (IFD).