What Is a High-Density Foam Mattress?

High-density foam means the foam is heavier and more tightly packed, measured in kilograms per cubic metre (kg/m3). The higher the number, the longer the mattress holds its shape, and anything under 21 kg/m3 sags fast. Mr Mattress builds on high-density cores from 45 to 65 kg/m3, and we print the number on every product so you can check it before you buy.

What density actually means

Think of a brick and a kitchen sponge. Same size, very different weight, because the brick is packed tighter. Foam works the same way. Density measures how much foam is packed into one cubic metre. More foam in the same space means more support and a longer life before it starts to soften.

It has nothing to do with how the mattress feels at first. A cheap, low-density foam can feel lovely in the shop. Density tells you whether it will still feel that way in two years.

High density vs cheap foam

Cheap foam is light because there is less in it. It feels fine for the first month, then your hips start to leave a dip where you sleep. Once foam loses its structure it does not come back, and you are back to mattress shopping. High-density foam carries your weight night after night and holds its shape for years. That is the whole reason we build the way we do.

Density is not the same as firmness

This trips up almost everyone. Firmness is how hard or soft the bed feels. Density is how much foam is inside it. You can have a soft high-density mattress and a firm low-density one. A salesperson who only talks about firmness is not telling you whether the bed will last. Ask for both.

How to read a mattress spec before you buy

Before you pay, ask one question: what is the foam density in kg/m3? If the seller cannot tell you, that is your answer, walk away. A good shop knows the number and prints it. For everyday sleeping you want 30 kg/m3 and up. For a main bed you will sleep on for years, look for a support core of 45 kg/m3 or more.

What we publish

We list the density of every model, in writing, on every product page:

Comfort Foam - firm, 45 kg/m3 core, supports up to 80kg, from R2,399
Active Foam - firm, 50 kg/m3 core plus a 27 kg/m3 top, up to 100kg, from R3,399
Revive Memory Foam - medium, 65 kg/m3 core plus a 30 kg/m3 memory top, up to 140kg, from R4,899
Hybrid Foam - medium, foam and spring build, up to 100kg, from R4,999

Every one comes with a 365-night home trial and free nationwide delivery, made in South Africa. If a price ever looks too cheap to be true, check the density. That is usually where the saving is hiding.

See the range →

Frequently asked questions

What is a good foam density for a mattress?

For everyday sleeping, look for 30 kg/m3 and up. Under 21 kg/m3 and you are buying a mattress with a clock on it, it will soften and dip within a year or two. Our support cores run 45 to 65 kg/m3.

Is high density foam good for a heavy person?

Yes. The denser the core, the more weight it carries without dipping. Our Hybrid and Active hold up to 100kg, and the Revive holds up to 140kg. There is a full breakdown on the best mattress for a heavy person page.

Does high density foam sleep hot?

It can hold more heat than a spring bed, because denser foam traps warmth and moves less air. A breathable cover, a foam that is not sealed in plastic, and natural-fibre sheets make the real difference. Soft memory foam runs the warmest, a firmer high-density foam sleeps cooler.

High density vs memory foam, what is the difference?

They are not the same thing. Density is how tightly packed the foam is, which controls support and how long it lasts. Memory foam is a type of foam that moulds to your body. You can get high-density memory foam or low-density memory foam, so always ask for the kg/m3 number, not just the name.