This shouldn't come as a surprise, but firmness varies from foam to foam. In the show room, you're usuallytold that one of three options constitutes the "soft" mattress offerings, while two others make up the store's "firm" selection. But what does that mean objectively?

To get to that answer, you need to know how firmness is measured. In the case of polyurethane foams this is determined by a physical property called the Indentation Force Deflection, or IFD. You may also hear it called the Indentation Load Deflection, or ILD. These are the same thing. While this can sound quite technical, all it refers to is the number of pounds of weight (or force) required to condense a 4-inch thick sample of the foam to 75% of its original height. Translation? The higher the IFD, the firmer the foam.

One important thing that we often note with foam is that, while IFD is the scientific measure of firmness, the level of resiliency or even the feel of the foam type can also sometimes play into an individual’s perception of firmness or softness. When it comes to feel, it’s not always apples to apples and, for this reason, we always encourage our customers to try their options prior to purchasing whenever possible. That is the best way to dial things in and people are sometimes surprised by what they like best. Below is a table showing the specifications (IFD included!) of each of our comfort layers.

Low-density foam in the base layer is a prevailing problem in the mattress industry and, as the numbers indicate, it will likely leave many people unsatisfied with the performance of their mattress over time.

On the opposite end of the spectrum, there has similarly proven to be negative performance associated with using foam that is too dense in the top layers of a mattress. While this material will surely last, too much density can result in overheating as a result of what has become known as the “oven effect.” Essentially, past a certain point, the level of density may create a totally unbreathable layer, which causes a sleeper’s body heat to be trapped all around them while they sleep. 

Fortunately, there is a sweet spot: a perfect level of density that is durable enough to last for 10+ years, but won’t create any heat issues (especially when paired with some sort of cooling technology, which we’ll outline in the next section) or any other performance related problems. That sweet spot lies in the 2.5-3.9 lbs/ft³ range, which has become a benchmark and industry standard for memory foams and top layers. Take a look at the following chart, which was compiled from a study of over 7,100 memory foam bed owner experiences, conducted by Sleep Like the Dead, an unbiased sleep-product review source: