What Foam Density Do I Need for Sofa Cushions?
Density is the single most useful number when you are choosing foam, and it is also the most misunderstood. It is not firmness, it is not comfort, and the figures quoted in American guides do not translate to what UK suppliers actually sell. Here is what it means and which of our foams to pick.
What foam density actually measures
Density is the weight of one cubic metre of foam, written as kg/m³. It tells you how much material is in the foam rather than how hard it feels. More material means more to compress, which is why density predicts how long a cushion lasts far better than it predicts how firm it feels on day one.
This is why a cheap sofa can feel perfectly comfortable in the showroom and sag within a year. It was not the wrong firmness. It was low density foam with not enough material in it to recover.
Why the numbers you find online often do not match
Search for foam density and you will find charts saying you need 40–50 kg/m³ for a sofa. Those charts are almost always American, where density is quoted in pounds per cubic foot and converted, and where the foam formulations differ.
UK upholstery foam works on a different scale. Standard domestic seating foam here typically sits in the high twenties to mid thirties. Foam at 40 kg/m³ and above exists, but it is contract and commercial grade — the sort specified for pub benches, waiting rooms and cinema seating that take hundreds of people a week.
So if a guide tells you a home sofa needs 45 kg/m³, it is not lying, it is answering a different question in a different market.
Our three foams, and what each is genuinely for
White — 28 kg/m³
A softer foam. The right choice for back cushions, scatter cushions and bolsters, where you lean rather than sit and the job is comfort rather than support. Also used in mattresses where a softer surface is wanted.
We would not put it in a seat cushion that gets daily use. In a back cushion it will outlast the fabric.
Blue — 33 kg/m³
Our seating foam, and the one to choose for anything you sit on: sofa seats, dining chairs, window seats, benches and bay seating. This is standard UK domestic upholstery grade — the same class of foam a professional upholsterer would fit to a family sofa.
For an ordinary household sofa this is the correct specification, not a compromise. If you are furnishing something that takes commercial-level traffic — a cafe bench, a village hall — you want a contract grade above this, and we would tell you so rather than sell you the wrong thing.
Memory foam — 60 kg/m³
The highest density we cut, but it is a different material rather than a firmer version of the other two. Memory foam softens with body heat and moulds to your shape, then recovers slowly. That is excellent for mattresses, toppers and pressure relief, and wrong for a sofa seat, where you want the cushion to push back rather than sink.
Do not read 60 as "twice as good as 33 for seating". Read it as "a different job".
Density is not firmness
Two foams at the same density can feel quite different, because firmness is set separately during manufacture. Density tells you how long it lasts. Firmness tells you how it feels the first time you sit down.
The practical consequence: a soft, dense foam is a perfectly sensible thing to want, and a firm, low-density foam is the one to avoid. Firmness without density is a cushion that feels supportive in the shop and flat by spring.
How to choose, in one line
If you sit on it, choose Blue. If you lean on it, choose White. If you sleep on it, choose White or Memory.
Almost every order fits one of those three. Where people go wrong is putting a soft back-cushion foam into a seat because it felt nicer when they squeezed a sample — the seat carries your whole body weight every single time, and that is the cushion that fails first.
A note on thickness
Density and thickness are separate decisions, and thickness matters more than people expect. A 5 cm seat pad in the right density will still bottom out; the same foam at 10–12 cm will not. As a rough guide: seat cushions 10–15 cm, back cushions 8–12 cm, seat pads and benches 5–8 cm.
Getting the size right
Once you have chosen a density, the next thing to get right is the measurements — and the usual mistake is measuring the old foam rather than the cover. Our guide on how to measure foam for cushions walks through it.
When you are ready, you can order foam cut to your exact size in any of the three densities above, or read more about replacing sofa cushion foam if that is the job in hand.
Order your foam
Once you know the density you need, order it here:
- Foam cut to size — 28, 33 and 60 kg/m³, cut to your measurements
- Replacement sofa cushion foam
- Upholstery foam cut to size
Not sure how to measure? Read how to measure foam for cushions.