Underlay is the cheapest upgrade in flooring that makes the biggest difference — and the one people most often skimp on. It's hidden, so it's tempting to spend the budget on the bit you can see. But the underlay is what your floor actually sits on every day, and the right one makes a carpet feel softer, last years longer, feel warmer, and sound quieter. The wrong one — or the wrong type entirely — can ruin a good floor and void its warranty.
The single most important thing to understand is that there is no such thing as one "good" underlay. The best underlay depends entirely on what's going on top of it, what's underneath it, and how the room is used. Let's break it down properly. (Once you know the types, our companion guide on the best underlay for every room tells you exactly what to put under stairs, bedrooms, heated floors and laminate.)
This is the mistake we see most often. Underlay falls into two completely different families, and they are not interchangeable:
⚠️ Never lay laminate or engineered wood over soft carpet underlay. The thick, squashy foam lets the floor flex with every step, which works the click-joints loose and causes the planks to split or "ping" apart within months. It's one of the most common DIY mistakes — and it isn't covered by any warranty.
Good carpet underlay does four jobs at once: it adds cushioning so the carpet feels luxurious underfoot, it absorbs daily footfall so the carpet wears more slowly, it adds thermal insulation (warmth), and it deadens sound. You can browse the types we stock on our underlay page, but here's how to actually choose.
The most common and affordable choice — made from recycled foam offcuts. It's measured by density (in kg/m³): the higher the density, the better the support and the longer it lasts. A good all-rounder for most bedrooms and living rooms.
More resilient and harder-wearing than foam, with a luxurious feel. A common choice for living rooms and a sensible pick where you want underlay that bounces back over many years. Generally works well with underfloor heating.
Premium, dense, heavy underlay made from recycled tyre crumb. Exceptionally durable and a favourite under quality wool and saxony carpets — and very good on stairs and high-traffic hallways because it doesn't break down.
Firmer underfoot with excellent thermal insulation. Often chosen for traditional woven carpets and properties where warmth matters most. Less bouncy than rubber or foam.
People often assume the thickest underlay is the best. It isn't. Most carpet manufacturers specify a maximum thickness — commonly around 11mm — and going thicker than the carpet is rated for can actually void the warranty. Too much cushioning lets the carpet flex excessively, which stresses the backing and the seams and causes premature wear and rucking.
For most rooms, somewhere around 8–11mm is the comfortable sweet spot. What matters more than raw thickness is density: a dense 9mm underlay will support a carpet far better than a cheap, airy 11mm one. On stairs, choose a firmer, often slightly thinner underlay — too soft and the carpet won't grip the nosing safely.
💡 Rule of thumb: match the underlay to the carpet. A budget polypropylene carpet doesn't need a premium crumb-rubber underlay, but a good wool twist deserves one — it'll feel better and last years longer.
Laminate and most engineered wood are "floating" floors — they aren't fixed down, they rest on a thin underlay that sits between the planks and the subfloor. This underlay does a very different job from carpet underlay:
Hard-floor underlay is thin and firm — typically around 2–3mm. Always follow the flooring manufacturer's stated maximum; going too thick or too soft causes the same joint failure described above. The key features to choose between are:
💡 Some laminate and engineered boards come with a thin foam backing already attached. If yours does, you usually only need a separate DPM over concrete — not a second underlay on top. Check the pack, or just ask us.
"Tog" measures thermal resistance — how much a material insulates. For warmth underfoot in an ordinary room, a higher-tog underlay is cosy. But with underfloor heating it's the opposite: you want the heat to pass up into the room, not be trapped below the floor.
The widely used guideline is that the combined tog of the floor covering plus the underlay should stay at or below 2.5 tog for underfloor heating to work efficiently. That usually means choosing a low-tog underlay (often around 0.5–1.3 tog). Rubber underlays tend to perform best over UFH; thick felt and standard PU foam have high thermal resistance and can effectively insulate your heating away from the room. For hard floors, choose an underlay specifically rated as UFH-compatible.
"Soundproofing" actually covers two different problems, and it's worth knowing which one you're trying to solve:
Acoustic underlays are tested for how many decibels (dB) of impact sound they remove. A good acoustic underlay can cut impact noise substantially, and manufacturers publish a dB figure for each product so you can compare like for like. The denser, rubber-based acoustic underlays generally perform best.
This matters most in flats and converted buildings. In England and Wales, Building Regulations Approved Document E sets legal limits on sound passing between separate dwellings. For impact sound through separating floors, the limit is broadly 62 dB for new-build and 64 dB for conversions (lower is better). If you own a leasehold flat, your lease may also require a minimum standard of acoustic underlay before you're allowed to fit a hard floor.
⚠️ Acoustic underlay on its own does not automatically make a floor Part E compliant — compliance depends on the whole floor build-up (the structure, the underlay, the floor covering and the ceiling below). If you're in a flat, check your lease and, for conversions, speak to building control before you commit. We're happy to advise on the right acoustic underlay for the job.
Underlay made for a quiet bedroom is not the right product for a busy office, shop or hallway in a let property. Commercial and heavy-traffic settings need a denser, more dimensionally stable contract-grade underlay that won't compress, shift or break down under constant footfall and the weight of office chairs.
If you're fitting out a shop, office or rental in the area, our commercial flooring page covers the contract options, and we'll spec the right underlay as part of the job.
| Situation | What to choose |
|---|---|
| Bedroom / lounge carpet | PU foam or sponge rubber, ~8–11mm, medium-to-high density |
| Quality wool / saxony carpet | Premium crumb rubber (e.g. Cloud 9 type) |
| Stairs & hallways | Firmer, often slightly thinner, high-density underlay |
| Laminate / engineered wood (floating) | Thin (2–3mm) firm hard-floor underlay; add DPM over concrete |
| Underfloor heating | Low-tog underlay; combined floor + underlay ≤ 2.5 tog |
| Flat / room above another dwelling | Acoustic underlay with a published dB rating; check the lease & Part E |
| Office, shop, busy let | Contract-grade high-density underlay, or carpet tiles with no underlay |
When we come to measure up in Hastings, St Leonards, Bexhill or anywhere across East Sussex, we'll look at your subfloor, your chosen floor and how the room is used, and recommend the right underlay for your situation — including whether you need a damp-proof membrane or an acoustic spec. Underlay is included in our fitting quotes, so there are no surprises. There's no pressure and no obligation.
Book a free home measuring visit and we'll advise on the right underlay at the same time — no charge, no obligation.
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