Understanding Foam Density and Firmness and Their Differences

The density of a foam item indicates its quality, and is found by measuring the weight of a foam sample block in a standardized size. The weight of the block is registered in pounds and is directly translated as the material’s density value. That means, if the foam product weighs two pounds, the density of the given foam is two pounds as well. In higher density foam, like the kind used to make exercise mats and firm mattresses, the cube weight and density rating are often five or six pounds or more. The reason this assessment is indicative of quality is because the tested blocks are always the same size, so a material packing more weight into the same space obviously contains more performance material. Lighter foam has more air in their form, meaning less performance material and less durability.

Firmness is measured and translated in a completely different way. A section of foam, again cut to a standardized size, is compressed by 25 percent of its thickness. For uniformity, samples are almost always four inches thick, making 25 percent compression equal one inch. The amount of force required to compress to that point is applied in the form of an Indentation Load Deflection (ILD) rating. That means if the sample of foam has a 10 ILD, it required 10 pounds of pressure to compress the sample by the aforementioned 25 percent. Taking more weight to reach the required compression level means it is a firmer material. For real-world example of applying this value, take somebody looking for a firm couch cushion. They would want to find a foam with a higher ILD rating, about 30ILD or greater.

These two values can exist in any combination; high ILD/low density, high density/ILD, or a balance of the two and so on. It’s important to know your product preferences beforehand, and you can then use these two foam values to help ID the right products for you.