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What is Indentation Load Deflection?


Buying a mattress requires quite a bit of research. Even when you have narrowed it down to just one mattress material there are still lots of different types within one material for you to choose from. Because you are going to spend a third of your time on this mattress, it makes sense to choose the best you can.

If you have decided to get a memory foam mattress (the best there is!) then you might notice many manufacturers refer to indentation load deflection (ILD). Indentation load deflection measures how hard or soft the memory will be. It is calculated by measuring how many pounds of pressure it takes to indent a four inch think piece of memory foam by 25%. This test is done by applying the pressure across an area of 50 square inches. The amount of pressure required is then converted into a weight. The indentation load deflection number you see on various mattresses is that weight.

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. If a mattress has a rating of 12, this means it takes twelve pounds of pressure to indent the mattress by 25%.

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

Generally speaking, the higher the indentation load deflection the better the mattress.

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