7) What does the 'ILD' rating tell me about a memory foam mattress and why is it important?

The density and ILD rating of a memory foam mattress provides the best indication as to the quality and firmness level you should expect from the mattress.

'ILD' stands for 'indentation load deflection'.

Put simply, it indicates how hard or soft the memory foam will be.

This is calculated by measuring how many pounds of pressure are required to indent a 4" layer of memory foam by 25%. The test is performed by applying equal pressure over an area of 50 square inches to indent the memory foam by 25%. The amount of pressure required to indent the foam by 25% of its total depth is calculated in weight.

To make sense of this, and better understand the ILD rating of a memory foam mattress, please see our example below:

It may take 8lbs of pressure to indent a very soft memory foam by 25%, or 20lbs of pressure to indent a very firm sample of memory foam.

You will often see the ILD rating expressed in a range, i.e. 10 - 12, as opposed to a single number. This is because the ILD rating can vary slightly depending on how the memory foam has been conditioned or the environment it has been stored in prior to testing. Moisture and humidity are two factors that can influence the slight variation in measurement, which is why many retailers display the ILD rating in a range format.

Our memory foam mattresses have an ILD rating of 13 - 15, or more accurately, 13lbs - 15lbs - putting them in the category of medium to firm.