Customer confuse foam density and foam softness all the time. They write email to me, “I’m looking for a low density foam.” I always ask “Do you really mean density or do you mean softness?” They (almost always) mean softness.
So, what is the difference? The density of foam is a measurement of theweight of a cubic volume of a material, like 12lbs/ft3. On the other hand, the softness of foam is a measurement of the tension on the surface of the material when it is touched.
Actually, there is not a real direct relationship between foam density and foam softness. You can have foam that is 2lb/ft3 density and is very soft or very hard. It depends on the chemicals used to make the foam.
How, then, is softness measured? It’s measured with an instrument called a durometer. There are three major softness measurement scales: Shore 00 (shown right), Shore A, and Asker C. Shore 00 is the best scale to use when you want to measure something that is very soft as it has the widest scale on the soft end.
So, is there any relationship between softness and density? Not really. However, there is a direct relationship between density and Squishiness (a new term I have created.) Of course, I’ve had to also create the tool for measuring this soft foam specification…the Squishometer (seen below left.)
Take the difference between open cell foam and closed cell foam. Open cell foam scores extremely high on the Squishometer because it has a very low density. (A sponge is an example of open cell foam.) Closed cell foam tends to be denser and, therefore, scores low on the Squishometer.
Hopefully my short post on this (often confused) physical property of soft foam is now clear. The next customer who asks me will be the test of this theory.