Written by the Carpet Flooring Supplies team
Practical buying guidance based on manufacturer specifications and our experience supplying carpet underlay nationwide.
Choose carpet underlay in this order: confirm the carpet and fitting requirements, check any underfloor-heating restrictions, then match the product to the room's traffic and the feel you want. Thickness, density and material help you compare suitable products. None of them is a complete quality rating.
A soft bedroom, a busy staircase and a heated lounge need different checks. This guide brings those decisions together and links to the detailed comparisons, so you can build a shortlist and order the right quantity.
Which underlay suits your room?
Use the table as a starting point, then check the named product's current technical information and the carpet manufacturer's instructions. On a small screen, scroll sideways.
| Room or requirement | What to prioritise | Next guide |
|---|---|---|
| Bedroom | A compatible domestic grade with the cushioning you prefer; check door clearance and total floor height. | Compare underlay thicknesses |
| Lounge or dining room | Support appropriate to traffic and furniture, as well as comfort. Busy routes deserve closer attention than little-used corners. | Compare PU foam and rubber |
| Stairs, landing or hallway | Firm, resilient support and an explicit recommendation for the use. Confirm thickness and fitting with your fitter. | Choose stair underlay |
| Room with underfloor heating | Approval for the exact heating system and a complete floor covering within its thermal-resistance limit. | Choose UFH underlay |
| Upstairs room with footstep noise | Relevant impact-sound test data and suitable support; assess the wider floor construction if noise is a major problem. | Understand acoustic underlay |
Start with the carpet and fitting method
Find out whether your carpet requires a separate underlay and which constructions are approved. Backing, carpet construction and fitting instructions can rule out products before comfort or price comes into the decision. A product sold for laminate or another hard floor is not automatically a substitute for carpet underlay.
In a stretch-fit installation, gripper holds the carpet over the underlay. A double-stick system bonds the underlay to the subfloor and the carpet to the underlay. Those are different specifications: the underlay, carpet and adhesives must be suitable for the chosen method. Interfloor's installation-method guide explains the distinction.
Give your fitter the exact product names before ordering. Ask them to confirm the underlay, gripper or adhesive system, seam layout and finished floor height. Resolve damp, movement or unsuitable subfloor conditions before installation; more cushioning is not a repair for a poor base.
PU foam, crumb rubber or sponge rubber?
PU foam offers many cushioning and density options and is generally easier to handle than dense rubber. It is a useful starting point for bedrooms and lounges, with appropriately rated high-density grades available for heavier use.
Crumb rubber has a dense, granular construction and typically feels firm. Products specifically rated for concentrated traffic can be useful on stairs and landings or beneath heavy furniture.
Sponge rubber is a cellular construction. Its range includes springy domestic products and specialist low-tog options. It is different from crumb rubber; the word “rubber” alone does not establish comfort, thermal performance or fitting suitability.
Other constructions, including felt and combinations, serve particular carpet and installation needs. Check their specification rather than forcing every choice into a foam-versus-rubber comparison. Our material guide explains the main differences in more detail.
Three examples of choosing by specification
These are examples from the CFS range, not a universal shortlist for every home.
- Tredaire Chromium is a 9mm, 180kg/m³ PU product specified for stretch fit and heavy contract use. It illustrates why foam should not be dismissed when support and demanding use matter.
- Tredaire Treadmore is a 7.95mm crumb-rubber product. Interfloor specifically promotes it for stairs, landings, heavy furniture and high foot traffic.
- Duralay Heatflow Carpet is a 6.1mm sponge-rubber product with a 0.75 tog rating for compatible heated-floor applications. It is not recommended for electric mat or dry UFH systems; low tog does not override that restriction.
Manufacturer references: Chromium, Treadmore and Heatflow Carpet, including their linked technical sheets.
How thick should carpet underlay be?
Choose an approved thickness that works with the carpet, room and finished floor level. A deeper underlay can contribute to cushioning, but the carpet and material also affect the feel. Maximum thickness is not automatically the best choice for a staircase, a tight doorway or a carpet that needs firm support.
Density is mass per unit volume. It can help compare similar constructions, but a dense crumb rubber and a lighter PU cannot be ranked fairly by their density figures alone. Intended use, recovery and installation requirements matter too.
Read 8mm vs 10mm vs 12mm carpet underlay for the full thickness comparison. If you are narrowing the choice by brand, Cloud 9 vs Tredaire compares named products rather than assuming one range always wins.
Do you want to resist heat loss or let floor heat through?
Tog measures thermal resistance. A higher tog resists heat passing through the floor covering more strongly. That may be useful over an unheated floor; over underfloor heating, it can restrict the heat you want to reach the room.
For UFH, check the complete carpet, underlay and any other required layers against the exact system's permitted thermal resistance. Also check product approval, temperature limits and the required floor build-up. A commonly quoted combined tog number is not permission to ignore the system instructions.
For example, a hypothetical 1.0 tog carpet plus a 0.75 tog underlay totals 1.75 tog before any other relevant layer. Whether that combination is acceptable depends on the specific system and products.
Use underlay tog ratings explained to understand the figures, then read the underfloor-heating buying guide before choosing from our UFH underlay range.
What if reducing noise is the priority?
Carpet underlay can cushion impacts such as footsteps. Published impact-sound figures describe laboratory test conditions; they are not guaranteed reductions for every noise in your home. The carpet, structural floor, ceiling, junctions and fitting affect the result.
Compare results on the same test basis where possible. A small difference between two headline dB figures does not by itself establish which will work better in your room. Voices, music, squeaks and structural noise may need different solutions. Our acoustic-underlay guide separates impact sound from airborne sound and explains the limits.
Plan the quantity and complete order
Underlay is supplied in rolls with different widths and areas. Measure the rooms, allow for the actual cutting plan and divide by the exact roll coverage. Round up to the next whole roll when the product is sold only in full rolls. The area calculation is a starting estimate; narrow strips, stairs and awkward shapes can change what is usable.
Our underlay quantity guide and calculator helps with the arithmetic. Buying carpet as well? Follow how to measure a room for carpet: carpet roll width and pile direction mean you should not simply order the same square metres for both materials.
If you hope to keep an existing underlay, use our reuse and replacement checklist. Check its condition across the room and compatibility with the new carpet; an unworn edge does not prove that the main walkway is still supportive.
Compare the whole order cost, including delivery and the correct number of rolls. Arrange measuring and fitting separately: Carpet Flooring Supplies is an online, nationwide supply-only business.
Your final buying checklist
- Confirm the carpet accepts the chosen underlay and fitting method.
- Check any UFH approval, thermal-resistance and temperature requirements.
- Match the product's intended use to the busiest part of the room.
- Check thickness, finished height, thresholds and door clearance.
- Compare comfort, tog and sound information without treating one number as a quality score.
- Confirm room measurements, strip layout, full-roll coverage and total delivered cost.
Frequently asked questions
Can I use the same underlay throughout the house?
You can if the exact product meets every room's carpet, use and fitting requirements. Check stairs and any heated rooms separately; simplifying the order should not create an unsuitable installation.
Is thicker underlay always more comfortable?
Not necessarily. Material, density and the carpet above it affect the feel. Choose within the carpet's approved specification and check the combined height before deciding on extra depth.
Is rubber better than PU foam?
Neither material wins everywhere. Firm crumb rubber, springy sponge rubber and PU foam offer different constructions and product choices. Compare the intended use and technical requirements first.
What underlay should I buy for stairs?
Start with a product explicitly suitable for concentrated stair traffic and the chosen carpet. Firm support and recovery matter more than choosing the thickest roll. Ask your fitter to confirm the installation details.
Can I use low-tog underlay with any underfloor heating?
No. Low tog is only one check. The product must be approved for the exact system and the full floor construction must meet its requirements. Some low-tog products exclude electric mat or dry systems.
Does an acoustic underlay make a room soundproof?
No. It can help reduce impact transmission, but it cannot guarantee silence or solve every airborne or structural noise problem. Assess the whole floor if acoustic performance is critical.