Foam ILD stands for Indentation Load Deflection, and it is the measure of the stiffness or how much force is needed to compress the foam.
The higher the ILD the harder the foam, and a lower ILD rating translates to a softer plush foam. Foam used in mattresses ranges from a 16.5 ILD for Plush, and over 44 ILD for Extra-Firm.
The ILD rating alone however is not a good indication of the firmness of a mattress. A thin piece of foam with a high ILD may feel softer than a thicker piece of foam with a lower ILD. This is because when measuring ILD a standard test is performed using a 4” thick piece of foam and measured when compressing the foam by 1”. Thicker pieces of foam provide more support than thinner pieces.
Unless you are a mathematician, it is best to try the mattress in store to get a true idea of the firmness.
