Carpet underlay has a bigger say in how a carpet behaves than most people expect, and the number everyone asks about is thickness. The answer is rarely just "thicker is better".
This guide explains what carpet underlay thickness does, how the main types of underlay differ, how to think about thickness room by room, where stairs and underfloor heating need extra care, and what our own deals include.
There is no single right thickness. Our deals include a free 8 mm (Silver), 9 mm (Gold) or 11 mm (Platinum) carpet underlay. Thicker feels softer, but loop pile, stairs, door clearance and underfloor heating can all call for something firmer or thinner, so choose it with the carpet and the room.
What carpet underlay thickness does
Carpet underlay sits between the carpet and the floor. Its job is to make the carpet feel comfortable, to help it last, and to add some insulation and sound reduction between rooms. A thicker carpet underlay usually feels softer and springier underfoot. A thinner one feels firmer. Neither is right for every carpet, which is why the thickness is chosen with the carpet in mind.
Underlay is the bit nobody sees and everybody feels.
Our own FAQ page puts it plainly: underlay affects the finish, feel and wear of your flooring, and a good one can help reduce noise between rooms, add insulation and extend the life of the floor.
Carpet underlay thickness in our deals
On our full house deals page the underlay comes in three thicknesses, each free with its deal:
- Silver (£1,299): free 8 mm underlay and grippers.
- Gold (£1,499): free 9 mm underlay and grippers.
- Platinum (£1,899): free 11 mm underlay and grippers.
On the Budget and Bronze deals, underlay is available if you need it. Ask at the visit and we will tell you what it adds to the price, and which material it is.
Carpet underlay types
Thickness is only one part of the picture. The material changes the feel too. These are general traits, so check the product details for the one you are offered.
- PU foam. Polyurethane foam is light and springy and gives a soft, cushioned feel. The speckled kind made from bonded foam offcuts is widely used under domestic carpet.
- Crumb rubber. A denser, heavier underlay made from rubber granules. It feels firmer, and it is often chosen where there is a lot of foot traffic, such as a hallway.
- Rubber. Natural or synthetic rubber underlay is dense and hard-wearing, and it is often used where a firm, stable base is wanted.
There is no single best carpet underlay for every house. The best choice is the one that suits your carpet, your room and your heating, so ask us about it when you see the samples.
Choosing carpet underlay by room
Think about how the room is used before you think about the number.
- Bedrooms and lounges. These are rooms where you stand barefoot and sit on the floor, and a thicker underlay makes the carpet feel more cushioned. Our carpet thickness guide explains how pile and underlay work together.
- Hallways and busy family rooms. A firmer feel can suit a floor that takes a lot of footfall, so ask what we recommend with your chosen carpet.
- Upstairs rooms. Carpet underlay can help with noise between floors. Our guide to reducing noise between floors goes further.
The carpet decides too
Some carpets are fussier than others. Loop pile and Berber styles tend to do best on a firmer underlay, so a very soft, thick one may not suit them. Check the guidance for the carpet you choose, or ask us when you see the samples.
Door clearance
Carpet and underlay together raise the floor. Check the gap under your doors before you choose, because a thick underlay under a deep pile can leave a door catching, and older houses can have doors and floors that are not quite level. We can look at this at the visit.
Carpet underlay on stairs
Stairs need a more careful choice than a flat floor. A very thick underlay can make the edge of each step feel soft and let the carpet shift, so stair underlay is usually thinner and firmer than the one on the landing. Ask for advice about your own staircase before you decide, because the carpet and the stair edge both play a part.
Tog rating and underfloor heating
A tog rating measures how much a layer holds heat back. The higher the tog, the more it resists heat passing through. Carpet and underlay each have a tog value, and the two add together. If you have underfloor heating, a thick, high tog underlay can hold some of the warmth back, so a lower tog underlay is the usual choice over a heated floor. The heating maker will state a limit on the combined value of the floor covering, so check that guidance before you choose, and tell us about the heating when you book. Our guide to flooring and underfloor heating covers what works.
Fitting matters as much as thickness
A good carpet underlay laid badly still gives a poor result. It has to lie flat and be joined neatly, with no gaps and no ridges that show through the carpet. Our guide to laying underlay and carpet shows the steps, and our own fitters do this on every job.
Questions people ask
What thickness of carpet underlay is best?
It depends on the carpet and the room. Our deals include 8 mm, 9 mm and 11 mm underlay. A thicker one feels softer, and a firmer one suits some styles, such as loop pile. We can advise when you see the samples.
What is the standard thickness of carpet underlay?
There is no single standard, because the right thickness depends on the carpet, the room and the heating. Our deals use 8 mm, 9 mm and 11 mm. Whichever you choose, check the clearance under your doors.
Is 10mm underlay too thick?
Not in itself. 10 mm sits between the 9 mm underlay in our Gold deal and the 11 mm in our Platinum deal. What matters is whether it suits your carpet, your doors and your heating, so check the guidance for the carpet you choose.
Is 12mm underlay too thick?
It can be. 12 mm is thicker than any underlay in our deals, and a very thick underlay can feel spongy, can suit loop pile and stairs badly, and adds to the height of the floor at your doors. Check the carpet maker's guidance and ask us before you go that thick.
Is thicker carpet underlay always better?
No. Too soft an underlay can suit some carpets badly, and it is not the right choice for stairs. Choose it with the carpet and the room in mind.
Do I need underlay under a new carpet?
Yes. Underlay changes how the carpet feels and how long it lasts, so we advise one on every job.
Is underlay included in your carpet deals?
Silver, Gold and Platinum include free 8 mm, 9 mm and 11 mm underlay. On the cheaper deals it is available if required.
Can I use thick carpet underlay with underfloor heating?
Check the heating maker's guidance first, because underlay and carpet both resist heat. A lower tog underlay is the usual choice, and you should tell us about the heating when you book.
See the options in your own home
Carpet underlay is easier to choose when you can feel the carpet on top of it. We bring samples to you as part of our Home Showroom service and give you a free quote with no obligation. Put the kettle on, book a free home visit or call 0800 920 2092.
Related reading: What Carpet Thickness Is Best for Your Home Floors?.
