Underlay Types Compared
Not all underlay is equal. Compare foam, rubber, fibre and PU underlays for comfort, sound and durability.
Underlay rarely gets the attention it deserves, yet it has a huge effect on how a floor feels, sounds and lasts. The wrong underlay can undermine even a good quality carpet or LVT, while the right one genuinely extends the floor's life.
There isn't a single 'best' underlay — the right choice depends on the floor going on top of it, the subfloor beneath, and whether sound insulation or thermal performance matters most in that room.
Tog rating, which measures thermal insulation, is another factor worth understanding: a higher tog underlay retains more warmth, which suits ground-floor rooms without underfloor heating, but too high a tog rating under underfloor heating can significantly reduce the system's efficiency.
Foam underlay
PU (polyurethane) foam underlay is a common, cost-effective choice for carpet, offering decent comfort and thermal insulation for typical domestic rooms.
It's generally not the most durable option for very heavy traffic or long-term compression resistance compared with denser alternatives, so grade matters for busy households.
Rubber underlay (crumb and sponge)
- Crumb rubber underlay is dense, durable and excellent for sound insulation, making it a strong choice under carpet in busy areas or above living spaces.
- It has less 'bounce' than foam, giving a firmer, longer-lasting feel underfoot that resists flattening over time.
- It's a heavier product, which some fitters find adds to handling time, though the durability trade-off is usually worth it.
Fibre underlay
Fibre underlay, often made from recycled materials, is a firm, dense option that performs well under carpet in commercial or high-traffic domestic settings.
It compresses less over time than softer foams, which helps carpet keep its appearance for longer under furniture and in walkways.
Specialist underlays for LVT and laminate
LVT and laminate need thinner, denser underlays than carpet — usually a combined acoustic and moisture-management layer rather than a thick cushioned foam, since excess give under a rigid floor can cause joints to flex and fail.
Acoustic underlays designed specifically for hard floors help reduce impact sound transmission, which matters in flats and multi-storey homes.
Comparing the main types
| Underlay | Best for | Key strength |
|---|---|---|
| PU foam | Carpet, general domestic rooms | Comfort, cost-effective |
| Crumb rubber | Carpet, busy or noise-sensitive rooms | Durability, sound insulation |
| Fibre | Carpet, high-traffic or commercial areas | Resists compression, firm support |
| Acoustic hard-floor underlay | LVT, laminate, engineered wood | Sound reduction without excess give |
Underfloor heating and moisture considerations
If underfloor heating is fitted, the underlay must be rated for it — some foams insulate too well and reduce heat transfer into the room, so a UFH-specific product is essential.
In rooms with any risk of subfloor moisture, an underlay with an integrated damp-proof membrane can offer useful extra protection beneath resilient floors.
Matching underlay thickness to door clearances
Adding underlay changes the overall floor height, and a thicker underlay chosen purely for comfort can be enough to make internal doors catch where they previously cleared comfortably.
We measure existing door clearances against the combined height of the new flooring and underlay before confirming a specification, so any adjustment needed can be planned into the job rather than discovered afterwards.
Storage and handling on site also differ by type: rubber and fibre underlays are heavier and bulkier to move around a property than foam rolls, which is a minor practical point but one that can affect access logistics on upper-floor flats or properties with awkward stairwells during fitting.
Frequently asked questions
- Does a thicker underlay always mean a better carpet feel?
- Not necessarily — very thick, soft underlay under carpet can actually cause the carpet to move and wear unevenly. Density and durability matter more than thickness alone.
- Can I reuse old underlay when replacing my carpet?
- We wouldn't recommend it — underlay compresses and degrades with use, and reusing old underlay under new carpet usually shortens the new carpet's life and voids some manufacturer guarantees.
- What underlay is best for underfloor heating?
- A thin, UFH-rated underlay with good thermal conductivity is essential; standard thick foam underlay can insulate against the heat you're paying to generate, so always check the specific rating.
- Is rubber underlay worth the extra cost over foam?
- For busy households, stairs, or rooms above living spaces where sound matters, yes — its durability and sound performance generally justify the higher price over standard foam.
Keep reading
Deciding between carpet and LVT for a bedroom? Compare warmth, comfort, allergies and upkeep before you commit.
Wool or polypropylene carpet — compare feel, stain resistance, price and durability before you choose.
Click LVT or glue-down LVT? Compare stability, feel, subfloor needs and cost before choosing your fitting method.
See how we survey, prepare and fit carpet across Kent.
See how we survey, prepare and fit LVT across Kent.
Talk it through with a fitter, not a call centre
Ask us to recommend the right underlay for your floor and subfloor at a free, no-obligation survey — call 07702 737267.