Mattresses for heavier people: it is about wire gauge and density, not "firm
Most mattresses are designed and tested around an average adult, and the further you are from that, the sooner a standard mattress dips, softens and stops supporting you. If you are over about sixteen stone, or two of you together are over about thirty, the advice you will get is "buy firm". That is only a third of the answer.
What actually wears out
A mattress fails for a heavier sleeper in three places, in this order:
- The comfort layer takes a body impression. Low-density foam compresses further under more weight and recovers less. A 40 kg/m³ memory foam that would last five years for a nine-stone sleeper can dish in eighteen months under sixteen stone.
- The springs lose height. Thinner wire (1.6 to 1.8 mm) compresses further and fatigues faster under a heavier load. The middle of the bed settles.
- The edge collapses. Sitting on the edge every morning with more weight on a soft foam rail rounds it off within a year, and the sleeping surface gets narrower.
So the three numbers that matter are foam density, wire gauge, and what holds the edge. Firmness is a feel; those are what make it last.
The numbers to look for
| Standard | For a heavier sleeper | |
|---|---|---|
| Memory foam density | 50 kg/m³ | 60 kg/m³ and up |
| Support foam density | 35 kg/m³ | 40 to 45 kg/m³ |
| Base foam | 33 kg/m³ | 40 kg/m³ |
| Spring wire | 1.8 mm | 2.0 mm (1.9 on 2,000-spring units) |
| Edge | Foam rail 30 kg/m³ | Steel rod, or a 50 kg/m³ rail |
| Comfort layer depth | 3 to 4 cm | 5 to 6 cm, so you sink into it, not through it |
Note the last row. Heavier sleepers need a deeper comfort layer, not a thinner one, because you press further into it. A hard mattress with a thin top puts all the pressure on your hip and shoulder; a denser, deeper comfort layer over a firmer spring unit gives support and relief both.
"Firm" versus Firm tension
Firm on a box means a hard surface. Firm tension, from a maker who offers it, means the spring wire, base foam and edge rail are upgraded while the comfort layer stays the same. That is the honest version of what a heavier sleeper needs: the same feel on top, more hold underneath. It is why we recommend Firm tension over about sixteen stone, and why a topper does not solve support.
Couples with a weight difference
If one of you is much heavier, a single spring unit is either too hard for one or too soft for the other, and the lighter partner rolls towards the middle. Split tension, one spring unit per side under one comfort layer, is built for this. It is available in king and super king from makers who build to order; see split tension explained.
Weight limits
Some brands state a maximum weight per side, often 18 to 20 stone, above which the guarantee does not apply. Others say nothing, which is not the same as no limit. Ask, in writing. A maker who specifies wire gauge and densities can tell you what the mattress is built for; a maker who says "suitable for all" has not thought about it.
The base matters more for you
Slats no more than 7 cm apart, a centre rail on king and super king, and a frame that does not flex. A platform-top divan is the most supportive base for a heavier sleeper. A dipped or flexing base will dish any mattress.
How we build for it
The Bad Back Years in Firm tension is our build for heavier sleepers: 5 cm of 60 kg/m³ memory foam, 2,000 springs in five zones on 1.9 mm wire, a steel edge, a 40 kg/m³ base, and split tension available in king sizes. The densities are on the page because they are the answer to the question.
The short version
- Firmness is a feel. Density, wire gauge and the edge are what last.
- 60 kg/m³ memory foam, 2.0 mm wire, steel edge, deeper comfort layer.
- Firm tension, not a hard mattress.
- Split tension for couples who differ.
- Ask for the weight the mattress is built for, in writing.
Side sleepers and sore hips: what the top layer of a mattress has to do
Most people sleep on their side and most mattresses are not built for it. Why the hip and shoulder take the load, what pressure relief actually means, the mistake of going firm, and the numbers to look for.
Bought a firm mattress and it is too hard? Three fixes, cheapest first
A firm mattress that feels like a board is the most common mattress regret. Give it thirty nights, check the base, add the right topper, and know when a swap is the honest answer.
What does "orthopaedic mattress" actually mean? Less than you think
There is no standard, no test and no body behind the word. It usually just means firm, which is not what the evidence recommends for a sore back. What to look for instead, and the questions that get you a real answer.