Foam density, hardness & firmness in mattresses

Updated 2020: You may be wondering why so few memory foam mattress companies will divulge their data on the foams they use. Unfortunately, without this figure, it is near impossible to compare or even know what kind of foam mattress you are buying. Like we advocate throughout our mattress site, you should always ask a retailer or mattress seller about the exact specifications of all the fillings of your new bed before buying it.

Only this detail lets you work out how suitable and appropriate any given mattress will be for you. Read on for more tips when it comes to memory foam mattresses.

Mattress foam grades explained

Memory, Hybrid and Latex foam mattresses use different measurements for mattress firmness when compared to traditional pocket spring mattresses. The foam grades are often completely hidden by retailers, mainly so you can’t compare mattresses when choosing a new bed. We explain the measurements you need to know when researching new foam mattress grades.

Density of mattress foam

The density of a foam refers to the weight of the foam in kilograms per cubic metre. High density foam mattresses have more foam per cubic meter than lower density foams. Simply put, you get more foam for your money. The more foam, the higher the resistance to loss of hardness and the more resilience there is to stress.

Usually, the higher the density of the foam, the firmer the foam’s support level.

Hardness of mattress foams

The hardness of foam is a measurement that gives a perceived firmness rating for a customer (i.e. the harder the foam is, the firmer it will feel). This is where density being the only measure of support is inaccurate. You need to also know the hardness.  Hardness is measured in a set range of tolerance and is not a one size fits all figure. It is worked out by compressing a piece of foam to 40% of its original size.

This measurement is then displayed in newtons (N) so a hardness rating of 70-100N means it takes between 70 and 100 newtons of pressure to compress it to 40%. The higher the figure the more force is needed and, therefore, the firmer the foam.

High density mattress foams explained

The only way to accurately work out the firmness and quality of foam is to know both the density and the hardness. The density shows the amount of foam and the hardness gives the firmness. You also need to know the desired feel or reaction of the foam (i.e. you could have a very hard foam mattress that is very responsive and ‘springy’, like Laygel).

So, although it’s got a high hardness rating, the manufacturing method means the end result is a somewhat ‘bouncy’ foam. You need to know the way the foam is intended to react: fast response, slow compression or supportive, for example.

If you don’t have these measurements and descriptions, you’re only really guessing. For example, you could have a 60kg foam with a hardness of 40-70N and a 40kg foam with a hardness of 70-100N, so the less dense foam would be firmer, but the 60kg softer foam would have high resilience as there is more foam within it.