Foam Grades Explained: Density, Firmness & Hardness

The easiest way to choose cushion foam is to work through the job in order: measure the cover, choose the thickness, then compare foam grades for how the cushion will be used.

If you are still working out the size, start with our cushion cover measuring guide. If you are unsure how thick the foam should be, see the foam thickness guide.

Once you know the size and thickness, this guide explains the foam grades shown in our foam cut to size calculator.

The Short Answer: Density Is Not Firmness

In a standard foam grade such as N31-190, the two numbers tell you different things:

Density is mainly about how much foam material is in a cubic metre and is closely linked with durability.

Hardness is the technical measure of how much force is needed to compress the foam. Firmness is the everyday way we describe how soft or firm that foam feels when you sit or lean on it.

This is why a higher-density foam is not automatically a firmer foam. You need to consider both parts of the grade.

What Does Foam Density Tell You?

Foam density is measured in kilograms per cubic metre, written as kg/m³. In simple terms, it tells you how much foam material is in the foam.

Higher-density grades will generally hold their shape and support for longer than lower-density grades used in the same type of application. That does not mean the highest-density option is always the right one. The cushion still needs to suit the job, thickness and feel you want.

What Do Hardness and Firmness Tell You?

The hardness rating tells you how resistant the foam is to compression. A higher hardness number generally means a firmer feel.

For example, two foam grades can have similar density but feel quite different when compressed. That is why choosing only by terms such as “high density foam” can be misleading.

Firmness is also not the same as quality. A very firm foam is not automatically more durable, and a softer foam is not automatically lower quality. The grade needs to suit how and where the cushion will be used.

Which Foam Grade Should I Start With?

These are starting points, not universal rules. In the foam cut to size calculator, choose the application that best matches your project and compare the recommended grades for your thickness and intended use.

You can also see the full foam grade reference for the density, hardness and resilience details of every grade we cut to size.

Why Thickness Changes How Foam Feels

The same foam grade can feel different at different thicknesses. A deep cushion has more foam to compress, while a thin cushion reaches the surface underneath much sooner.

That is why the foam grade should not be chosen in isolation. Set the cushion thickness first, then compare the grades that suit that application. Our foam thickness guide explains the support trade-off in more detail.

What About Outdoor Cushions?

If the cushion will regularly get wet from rain, pool use or marine conditions, start with reticulated outdoor foam rather than standard indoor upholstery foam.

Reticulated foam has an open structure that allows water to move through it. The calculator can help narrow the choice between softer and firmer outdoor grades based on how the cushion will be used.

Next Step: Choose the Finish

Once you have chosen the foam grade, the next decision is whether the finished cushion needs Dacron wrap, a foam overlay or just the foam itself. See our Dacron wrap vs foam overlay guide before adding the finish to your order.