Mattress Foams – Density vs. ILD

What’s the difference between 3lb. memory foam and 5lb.?

How about 24 ILD and 36 ILD?

What does ILD even mean?

Let’s start by letting you know that density and ILD are not the same thing. They are two different characteristics to describe the quality of foam. Density refers to how much the foam weighs and ILD is the firmness of the foam.

A 5lb density foam refers to the weight of a cubic foot block of foam, which is 5lbs. The higher the density, the higher quality and more expensive the foam. A 4lb density is 20% lower in quality than 5lb. These numbers are so close the difference is normally perceived as marginal to customers and often times trigger a customer to save a couple hundred dollars on a mattress by opting with 4lb density foam. This is fine as long as a customer understands the product won’t last nearly as long as 5lb foam.

ILD stands for indentation load deflection. An ILD machine pushes into foam and measures how soft or firm it is by how hard it pushes back (deflects) at a certain depth (indentation). ILD is not a measure of quality. The raw cost of 14 ILD foam and 36 ILD foam is the same. Consumers should not worry about ILD, they should only worry about how the overall mattress supports them – that it provides good postural alignment.

In conclusion, foam density is extremely important in determining the quality and durability of a foam. ILD has nothing to do with the quality, but everything to do with how a foam feels.



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