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glossary

ILD / IFD Foam Hardness

Entity: ILD IFD foam hardness

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In short

ILD (Indentation Load Deflection) or IFD (Indentation Force Deflection) measures how hard foam feels. It uses the force needed to compress foam a standard amount. Higher ILD means firmer foam. Density (kg/m³) is separate and relates more to durability. Mattress firmness also depends on thickness, layering, and the base beneath the foam.

Definition. ILD or IFD measures the force needed to indent foam a set percentage of its thickness. It is a hardness number, not density and not mattress firmness alone.

See also firmness and sleep position and memory foam materials.