Everything you actually need to know before you buy carpet underlay
You want to know which underlay to buy, how thick it should be, and what a fair price per square metre looks like.
Underlay is the layer that decides how your carpet feels underfoot and how long it survives. For most homes an 8mm to 11mm PU foam at around 100 to 140kg per cubic metre is the sensible choice, crumb rubber suits stairs and busy hallways, and you should expect to pay for it separately from the carpet on any honest quote.
Written for: Anyone buying carpet who has been handed a one line underlay price and told not to worry about it.
What underlay is actually doing down there
Underlay is not padding for comfort alone. It takes the compression of every footfall so the carpet pile does not take it, which is why the same carpet can look tired in three years on poor underlay and fine in ten on good underlay.
It also does three quieter jobs: it evens out small imperfections in the floorboards or screed so they do not print through the carpet, it slows heat loss downwards, and it dampens footfall noise between floors. In a flat or a converted house that last one matters more than people expect.
The four underlay types you will actually be offered
Ignore the brand names for a moment. Nearly everything sold in the UK falls into one of four families, and the family tells you more about performance than the label does.
- PU foam, made from recycled furniture foam. Light, warm, springy and the most common domestic choice. Good all round, excellent value.
- Crumb rubber, made from recycled tyre rubber. Heavy, firm and very durable. The choice for stairs, hallways and anywhere with a heavy traffic pattern.
- Sponge rubber, either flat or waffle. Softer than crumb, traditionally paired with wool carpet, and still preferred by some fitters for a classic feel.
- Felt and felt combination, made from fibre. Firm and dense with a solid rather than bouncy feel, and often specified under loop pile because it stops the pile rolling.
Typical UK underlay prices per square metre
| Type | Usual thickness | Typical UK price per m2 | Best for |
|---|---|---|---|
| PU foam, standard | 8mm to 10mm | £3 to £6 | Bedrooms and general use |
| PU foam, high density | 10mm to 11mm | £6 to £10 | Living rooms, longer life |
| Crumb rubber | 8mm to 9mm | £7 to £12 | Stairs, hallways, heavy traffic |
| Sponge rubber | 8mm to 10mm | £6 to £11 | Wool carpet, traditional feel |
| Felt or combination | 8mm to 10mm | £5 to £9 | Loop pile and period floors |
| Low tog for underfloor heating | 6mm to 8mm | £6 to £11 | Heated floors |
Ranges are the general UK market spread, not a quotation. Ask us for the price of what is on the floor this week.
Thickness, density and tog, without the sales patter
Three numbers get quoted and only two of them tell you much. Thickness in millimetres is how deep the underlay is. Density in kilograms per cubic metre is how much material is packed into that depth. Tog is the thermal rating and only matters for heat.
Thickness without density is the trap. A cheap 11mm foam at 60kg can feel wonderful in the shop and flatten in a year. A 9mm foam at 140kg feels slightly firmer on day one and still looks new when the other one has bottomed out. If you only ask one question about underlay, ask what the density is.
Tog only becomes a live question with underfloor heating, where you want the whole floor build up, carpet and underlay together, to stay under about 2.5 tog so the heat can get through. Without underfloor heating, a higher tog simply means a warmer room.
What thickness for which room
There is no single right answer, but there is a sensible default for each part of a house, and it is driven by how the room is used rather than by how much you want to spend.
- Bedrooms: 10mm to 11mm PU foam. Low traffic, so comfort can win.
- Living rooms: 9mm to 11mm PU foam at a decent density. Comfort matters but so does recovery under furniture.
- Stairs and landings: 8mm to 9mm crumb rubber or a high density foam. Too soft and the nosing edge crushes and the carpet looks worn at the front of each tread.
- Hallways: 8mm to 9mm firm. This is the highest traffic floor in the house per square metre.
- Rooms with underfloor heating: a low tog underlay, typically 6mm to 8mm, chosen specifically for the system.
What underlay costs in the UK
Underlay is priced per square metre like carpet, and it is bought to the same metreage as the carpet rather than to the floor area of the room. Rolls are usually 15 square metres.
The ranges below are the honest spread you will see across the UK market in 2026. Warehouse-only pricing sits at the lower end of each band because we buy clearance stock direct and hold it here rather than ordering it in against your job.
Fitting underlay: gripper, tape and the bits nobody mentions
Underlay is laid inside the gripper rods, not over them, and the joins are taped so they cannot separate under traffic. On boards it usually goes down with staples, on concrete with adhesive or a tackifier.
If the floor is being lifted, this is the moment to fix squeaks and screw down loose boards. It costs almost nothing while the floor is open and it is a real nuisance afterwards. Gripper, tape, door bars and trims are the accessories that quietly appear on quotes, so ask for them to be itemised.
Reusing old underlay, and when it is genuinely fine
Fitters push back on this for a reason. Old underlay has already been compressed exactly where the old furniture and the old traffic route sat, so a new carpet lands on a floor that is soft in some places and flat in others, and it wears unevenly from the first week.
The honest exception is underlay that is only a year or two old, laid over a sound floor, in a room that has barely been used. Even then, have the fitter look at it before you decide, because the cost of getting it wrong is the price of the carpet, not the price of the underlay.
Bring your room sizes and we will price the carpet and the underlay separately
You will see exactly what each part costs instead of one lumped number, and we stock underlay, gripper, trims and door bars alongside the carpet.
Have a look at these
Common questions
- Is thicker carpet underlay always better?
- No. Density does the hard work, thickness does the comfort. A 9mm underlay at 140kg per cubic metre will outlast an 11mm underlay at 60kg, and on stairs the thicker soft one is actively worse because the tread nosings crush.
- How much underlay do I need to buy?
- The same metreage as the carpet, not the floor area of the room, because both are cut from fixed width rolls. Underlay rolls are usually 15 square metres, so most jobs round up to whole rolls.
- What tog underlay works with underfloor heating?
- Aim for the carpet and underlay together to come in under about 2.5 tog, which usually means a purpose made low tog underlay of 6mm to 8mm. Anything warmer insulates the heating away from the room.
- Can I put new carpet on my old underlay?
- We would not advise it unless the underlay is very new and the room has had almost no use. Old underlay is already compressed along the traffic route, so the new carpet wears unevenly from the start.
- Do you sell underlay on its own?
- Yes. Both warehouses are supply only as well as supply and fit, so you can buy underlay, gripper, tape and door bars without buying carpet from us.
- Which underlay is best for stairs?
- A firm crumb rubber around 8mm to 9mm, or a high density foam. Stairs concentrate all the traffic in the house onto the front edge of each tread, and a soft underlay lets that edge collapse.