Know Your Foam: the Difference Between Firmness and Density, and How it Affects Your Mattress

Indenter testing foam firmness for a mattress

When shopping for a mattress, it can often feel like your senses are overloaded with terminology and seemingly useless information and, as a consumer, it's important to stay informed. So, what is your mattress really made of? To help answer this question we thought we’d take some time to explain two of the most commonly misunderstood terms in the foam mattress industry: density and firmness. Contrary to popular belief, these words are not synonymous. Understanding what they mean will allow you to see through some of the haze and gain a better understanding of the product you’re buying.

So, first things first, what is meant by the term density? Many of us hear words like this and simply assume that it means the mattress is hard; however, that is not necessarily the case. When commenting on the density of foam, mattress companies refer specifically to the mass within a given sample. The basic gist is that the denser a mattress is, the longer it will last. To measure this mass, we cut foam into a cubic foot and then weigh that individual piece. The weight of the piece in pounds amounts to the measurement of its density. Simple stuff, right?

What about firmness? Isn’t that just density revisited? In short, no. Where density measures how much substance can be found in a given area of foam, firmness measures how that substance will react when weight is applied. How much does an object sink into the foam? How much bounce does it have? How long will the foam behave when pressure is applied? The measure of firmness in foam is referred to as IFD,  which stands for Indentation Force Deflection. Measuring IFD is exactly what it sounds like: We check to see how much force it will deflect without being permanently indented. To do this a small circular indenter is pressed into the foam with increased pressure until the foam is indented to 75% of its original height. The pounds of pressure applied to the foam constitute the IFD.

Understanding these two pieces of information can make a world of difference when buying a mattress. Here at Comfort Option, we manufacture a full array of mattresses for you to choose from. Some, like our Alpha model, are dense without being especially firm. Meanwhile other models available through our mattress customization program give the sleeper the firmness that they really crave in a mattress. Whatever your needs, we want to make sure that you can get what you want and know what you’re getting.