When looking at foam, one the biggest assumptions people make is that density and firmness go hand-in-hand. This is fueled by the fact that that this is true in most materials. But when dealing with foam, foam density and firmness are two separate indicators, and there is no tie between the two.
This is because when dealing with foam, you aren’t dealing with a single material. Foam is a general name for multiple materials, and not only different varieties of the same material; there are many different types of foam, and each type has its own varieties as well. A good way to think about foam is like pasta. Saying you had pasta for dinner can imply many different things. Not only are there numerous dishes involving pasta, there are plenty of types of pasta that can be used to make the same dish as well.
Density is a quality indicator for foam, and doesn’t impact the feel or touch of a material. Density is measured by the weight of a cubic block of a given material. The greater the density, the greater the amount of physical product in a foam type, meaning there is more material that will last longer. Since all foam types are measured by the same metric, greater densities mean the amount of open air and space in a material is less.
Firmness impacts the firmness and rigidity of that foam formulation. Whether there is more or less material in that tested cube (density) does not affect the physical feel of a particular material’s formulation. The higher the Indentation Load Deflection value, the firmer the material.
Simply put, foam types can be made with different pairings of density and foam across the board. The formulations used to make foam can be applied in innumerable ways, each producing a different and unique foam. Because of this, it’s important to remember both values need to be looked at independently when you’re considering a foam purchase to make sure you’re purchasing something that you actually want.