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What does the ILD rating of a memory foam mattress mean?

The second main figure you should be looking for when buying a memory foam mattress is its ILD rating.

ILD stands for Indentation Load Deflection. In simple terms it is a measurement of how hard or soft a foam is. In more accurate terms it's the number of pounds of pressure required to indent 4" of foam by 25% using a 50 square inch indentation. You may also see it referred to as the 25% ILD rating.

For example, this means that a 15lb ILD rating would mean that the foam needed 15lbs of pressure to indent it by 25%, and a 25lb ILD rating would mean it needs 25lbs to indent by 25%, so basically this means that the higher the ILD, the firmer the foam.

You can use the ILD rating together with the foam's density to gain a good idea of the overall make up and quality of the foam.

It is worth noting that due to the batch production process of memory foam, the measured ILD and density ratings can change from batch to batch. It is not unusual for a foam that rates at 10lb ILD to vary between 8lb and 12lb.


This can also vary depending on the temperature and environment the foam has been conditioned in prior to testing.

All our mattresses are given an ILD rating of between 13lb and 15lb.