Understanding Foam Density, Weight and Firmness

What is foam density?

In simple terms, foam density measures the strength of a piece of foam. It's usually given as a decimal indicating the number of pounds each cubic foot of foam can support. The greater the density, the more supportive the foam, but a greater density doesn't necessarily mean a firmer product, and density doesn't determine comfort either.

Density varies between products as each foam type has different properties, so foam can't be directly compared by density alone. Higher-density products tend to be more expensive than lower-density ones, and densities often range from 0.5 up to 6 or more.

What is foam weight?

Foam weight is the actual physical weight of the product, as you'd measure it on scales. Weight increases with density (a higher density means greater overall weight) and, naturally, with the thickness and size of the piece. A good example is a foam mattress: a denser mattress feels far heavier in transit than a lower-density version.

What is foam firmness?

When manufacturers or retailers talk about firmness, they mean a measure known as Indentation Load Deflection (ILD). Every foam product has an ILD rating, calculated by placing the foam under pressure: once it has compressed to 25% of its original thickness, the weight used to achieve this constitutes the ILD rating.

Foam density vs foam firmness

Density and firmness aren't directly related. A higher-density foam isn't automatically firmer, and a lower-density foam isn't automatically a squishy one – low-density foams can feel just as firm. Overall firmness is simply how much a foam compresses under pressure, measured as an ILD rating. When choosing density and firmness, consider the user's weight: a heavier person should opt for a mattress that's both denser and thicker, as a lower-density product won't provide adequate support. For more on choosing the right material, see our guide to open-cell vs closed-cell foam.

How to gauge foam density and firmness

A good manufacturer or retailer such as eFoam can tell you the density and firmness of any product, as it's determined at the manufacturing stage. You can also estimate density yourself: density equals weight divided by volume, that is, weight ÷ (width × height × length). Because firmness is measured under controlled conditions, we can provide the exact ILD rating of your product – though firmness is largely down to personal preference, so you'll only really know by trying a product.

How comfortable is high-density foam?

High-density foam is praised for being comfortable thanks to its supportive qualities. For most people it offers great postural support in chairs, sofas and mattresses, which is where it's mostly found. If you're weighing up cost, our guide to cheap vs quality foam may help. For advice on the right density and firmness for you, please contact us.