Upholstery Foam Sheets FAQs
Foam FAQs
Straight answers to the questions we get asked most. If you cannot find what you need here, call us on 01494 441177 — we have been supplying foam for over 40 years and we would rather talk it through than have you order the wrong thing.
Density and firmness
Does high density mean firm foam?
No. This is the single most common mistake made when buying foam, and it is worth being clear about.
- Density is measured in kilograms per cubic metre (kg/m³). It tells you how much material is packed into the foam. Density predicts how long the foam will last — a denser foam resists compression set, which is the gradual permanent flattening that makes an old cushion feel dead.
- Firmness is measured in Newtons (N). It tells you how much force it takes to compress the foam. Firmness predicts how the foam will feel to sit or lie on.
These are independent properties. You can have a dense soft foam and a light firm foam. Our own range proves it:
| Grade | Density | Firmness |
|---|---|---|
| 39S | 39 kg/m³ — one of our densest | 120N — one of our softest |
| 33H | 33 kg/m³ — less dense | 190N — much firmer |
The 39S is the denser foam and the softer foam. If you buy "high density" expecting firm, you may get the opposite of what you wanted.
What does "ILD 40% Newton" mean?
It is how foam firmness is measured in the UK. A sample of foam is compressed to 40% of its original thickness, and the force required to hold it there is recorded in Newtons. A lower number is a softer foam; a higher number is a firmer foam.
Every firmness figure we publish uses this method, so our grades can be compared directly against one another.
Why do American foam suppliers quote different numbers?
Because they use a different test, and this trips people up constantly.
| UK | US | |
|---|---|---|
| Firmness measured by | Compressing to 40% of thickness | Indenting by 25% |
| Firmness units | Newtons (N) | Pounds-force (lbf) — quoted as ILD or IFD |
| Density units | kg/m³ | lb/ft³ |
The numbers are not interchangeable. A US "ILD 35" is not comparable to a UK "35N", and a US "1.8 lb/ft³" is not comparable to a UK "35 kg/m³". If you have been researching foam on American sites and cannot make the figures line up with ours, this is why. Use our Newton figures to compare our grades against each other, and ignore US ILD numbers entirely.
How do I choose a firmness?
| Firmness | Feel | Suitable for |
|---|---|---|
| Around 55N | Very soft | Memory foam comfort layers, toppers. Not for support. |
| Around 120N | Soft | Sofa back cushions, headboards, scatter cushions. Not seat cushions. |
| 125–150N | Medium | Standard sofa and chair seat cushions. |
| 190–240N | Firm to hard | Firm seating, dining chairs, caravan and boat cushions, mattress support layers. |
Fire ratings
What is Crib 5?
Crib 5 is BS 5852 Ignition Source 5 — the UK furniture fire test. A small wooden crib of pine, held together with wood glue and conditioned in a warm dry environment, is used as the ignition source. It burns for around 200 seconds. It is the standard required for contract and commercial furniture, and for children's furniture.
"Crib V" and "Crib 5" mean the same thing — V is simply the Roman numeral.
Is Crib 5 the same as Class 0?
No, and this matters. They are completely different standards for completely different purposes, and they are routinely confused.
| Crib 5 | Class 0 | |
|---|---|---|
| Tests | Ignition resistance of furniture | Surface spread of flame on a building surface |
| Standard | BS 5852 Ignition Source 5 | UK Building Regulations, via BS 476 Parts 6 and 7 |
| You need it for | Sofas, chairs, mattresses, upholstered furniture | Wall and ceiling linings, ductwork, HVAC, plant rooms |
| Our product | All our upholstery grades | Fireseal Class 0 |
If you are re-covering a sofa, Class 0 is not the standard you need — Crib 5 is. If you are lining a plant room, Crib 5 is not sufficient — you need Class 0.
An honest note on Crib 5 certification
BS 5852 is a composite test. The certification applies to the complete assembly — foam, cover fabric and any interliner together — not to the foam in isolation. Foam that meets the standard is a necessary part of a compliant cushion, but the compliance of the finished item also depends on the cover fabric used with it. Anyone telling you that buying certified foam alone guarantees a compliant piece of furniture is oversimplifying.
What is UL94?
A US flammability classification for plastics and foams, released by Underwriters Laboratories. For low-density foam there are two ratings: HF-1 (stops burning within 3 seconds of ignition, afterglow under 30 seconds, burning drips permitted) and HF-2 (stops burning within 2 seconds, afterglow under 30 seconds, no burning drips). Our acoustic foam carries UL94-HF-1 alongside its Crib 5 rating.
Choosing and measuring
How thick should my foam be?
Measure the internal depth of the cushion cover, not the old foam. This is the most common measuring mistake. A cushion that has gone soft has already compressed — measuring it will give you a replacement that is too thin, and you will have the same problem again.
As a general guide: sofa and chair seat cushions 4"–6", dining chair pads 1"–2", headboards 1"–2".
Can I use the colour to identify a grade?
No. Colour helps us identify foam in our own factory, and it makes our fabricators faster — but it is not a grade. Two of the most widely used grades in the UK are both blue (our 33H and 39H), and they are different foams. One blue foam is not necessarily the same as another blue foam, here or anywhere else. Buy on the published density and firmness figures, not on the colour.
Can I choose the colour of my foam?
Our products come in a range of colours, but we cannot change the colour of a grade to suit a preference. If you specifically want a certain colour, buy the grade that comes in it — but do check the density and firmness are right for what you are doing first.
Which foam sheet is right for me?
Every product page publishes its density, firmness and fire rating, and says what it is for. To see every grade side by side, use our foam grade comparison. If you are still not sure, call us on 01494 441177 — we would rather spend five minutes on the phone than have you order the wrong foam.
New foam
Will my foam soften?
Yes, slightly. All polyurethane foam softens by roughly 10–15% during the first few weeks of use as the cell structure settles. This is normal and expected, and it is not a fault.
Why does my new foam smell?
New foam often carries a faint manufacturing odour. It is harmless and it dissipates. Airing the foam in a well-ventilated room speeds it up.
Why has my foam turned slightly yellow?
Polyurethane foam oxidises on exposure to light and air, which causes a gradual yellowing. It is a surface effect and it does not affect the foam's performance, density or firmness. It is not a defect.
Why does the colour vary slightly between sheets?
Minor colour variation occurs naturally between production batches. It does not indicate any difference in grade or performance.
Ordering and delivery
Can I order from outside the UK?
Yes. We have supplied foam to customers overseas many times. Please contact us before ordering so we can confirm shipping and delivery timings for your country.
How quickly will it arrive?
Next working day delivery is available to most of the UK on orders placed before the daily cut-off. Timings vary by area — see our delivery page for the detail.