Thick underlay is not good underlay. On stairs, it's actively bad. That surprises almost everyone who walks into our St Leonards shop, because every advert you've ever seen sells underlay the same way: thicker = more luxurious = better. It's the flooring world's most profitable misunderstanding.
Here's the truth. Thickness is comfort. Density is performance. They are two different numbers on the label, and the one nobody looks at — density, measured in kg/m³ — is the one that decides whether your carpet still looks good in eight years or is worn through at the door in three.
We've been fitting floors across Hastings, St Leonards and Bexhill for over 15 years, and if we could change one buying habit, it would be this: stop choosing underlay by squeezing it. A soft squeeze feels lovely in the shop. So does a cheap mattress. Give it a year of feet.
The carpet gets all the attention. The underlay does half the work.
This guide tells you exactly what to put under each room, with the numbers to look for. (For the basics of foam vs rubber vs felt, see our companion guide on how underlay types compare — this one is about matching them to rooms.)
If you remember nothing else, remember this checklist:
Now the why — because the why is what stops you being upsold the wrong thing.
Think about what a stair actually endures. Your entire body weight lands on the nose of each step — a strip a few centimetres wide — every single time anyone goes up or down. A family of four can put well over 50,000 footfalls a year down one staircase, all funnelled onto the same narrow edges. No other floor in the house takes punishment like it.
Put a thick, soft, low-density foam under that and it does what soft foam does: it bottoms out. The cushioning collapses on the step edge, the carpet flexes and grinds against itself, and the pile wears through right where everyone can see it. We get called out to re-carpet stairs years before the rest of the house, and tired underlay is usually an accomplice.
What you want on stairs:
💡 Smart money move: if the budget's tight, put the dense underlay on the stairs and hall and a cheaper one in the spare room — not the same mid-grade everywhere. Same total spend, years more life where it counts. Where you put your money matters more than how much of it there is.
Here's the flip side, and it's good news: in a bedroom, you can have the luxury cheaply. Bedrooms get a tiny fraction of the traffic of a hallway, most of it in bare feet or slippers. Durability barely matters. Comfort is the whole game.
This is where the 10–11mm deep, cloud-soft underlays belong. A good one transforms even a modest carpet — that sink-your-toes-in feeling people pay a fortune chasing is mostly the underlay, not the carpet. The specs worth noticing here:
A favourite trick of ours: pair an ordinary mid-range bedroom carpet with a premium 11mm underlay. It feels more expensive than a premium carpet on budget underlay — and costs less.
The lounge is the compromise room — real traffic (it's often the through-route to the garden or kitchen), but you still want comfort in front of the sofa. The answer is the firm all-rounder: around 9–10mm of PU foam at a middling density, roughly the 100kg/m³ mark. Enough give to feel good, enough body to hold its shape in the walkways.
One extra rule: if you've gone for a pet-friendly carpet because of the dog, match it with rubber or high-density foam — claws and zoomies are stair-grade punishment delivered horizontally.
Everything above praises insulation. Underfloor heating reverses the rules. Tog is a measure of thermal resistance — how well something stops heat passing through. Brilliant under a normal carpet. A disaster on top of your heat source.
Put a cosy 3-tog bedroom underlay over a heated floor and you've tucked your heating system in under a duvet: the room takes hours to warm and costs more to run. The numbers that matter:
⚠ Don't let anyone sell you a "luxury thick" underlay for a UFH room. It's the most common underlay mis-sell we see, and you pay for it twice: once at the till and then on every heating bill. If you're not sure what your carpet's tog is, ask — we'll do the arithmetic for you.
This catches a lot of people: carpet underlay and hard-floor underlay are not interchangeable. Not "not ideal" — incompatible.
Laminate and engineered wood are floating floors held together by click joints. Those joints are designed to sit on a thin, firm base of around 2–3mm. Lay them over soft 9mm carpet foam and every footstep flexes the boards; flex the joints enough times and they crack, the floor clicks and creaks, and the warranty won't save you because every manufacturer's instructions say the same thing: use the right underlay.
What to look for instead:
Still deciding between the hard-floor options themselves? Our LVT vs laminate guide covers that fork in the road.
If you live in a flat — and a lot of Hastings and St Leonards housing is converted Victorian terraces with neighbours below — underlay is also your soundproofing. Look for the impact sound reduction figure in dB: good comfort underlays reach the mid-40s, and in conversions, Building Regulations Part E makes acoustic performance a legal requirement, not a nicety.
The happy coincidence: the same thick, soft underlays that make bedrooms feel luxurious are also the quiet ones. One purchase, both problems. For rental flats, where carpets take a beating between tenants, our rental flooring guide covers the durability side.
"It's still got life in it" — it almost never has. Underlay compresses where people walk, so an old one carries the ghost of the old traffic pattern: flat trenches at the doorways and in front of the sofa, pressed into your brand-new carpet from day one. It can also hide grit, damp and worse. New carpet on old underlay is a new suit over old boots.
A carpet is only ever as good as what's under it. Underlay is a small slice of the total job, but it sets the lifespan, the feel, the warmth and the quiet of the whole floor. If you're choosing between a slightly nicer carpet and a properly better underlay, the underlay upgrade wins almost every time — and it's the cheaper of the two upgrades.
By now you can see why this fails: the stairs need density, the bedroom wants thickness, the heated kitchen-diner needs low tog. One product can't win three different games. Mixing underlays room-by-room isn't a luxury approach — it's the budget approach done properly.
| Room / situation | What to look for | The number that matters |
|---|---|---|
| Stairs & hallway | High-density foam or rubber, 8–9mm | Density ≥130kg/m³ |
| Bedrooms | Thick, soft comfort underlay | 10–11mm, ~3.0 tog, 40dB+ |
| Living room | Firm all-rounder PU foam | 9–10mm, ~100kg/m³ |
| Underfloor heating | Heat-flow underlay, low resistance | ≤1.0 tog (≤2.5 tog incl. carpet) |
| Laminate / engineered wood | Thin, firm hard-floor underlay; DPM on concrete | 2–3mm |
| LVT | Follow the product spec — often none needed | Check first |
| Flats / upstairs | Acoustic-rated underlay (Part E in conversions) | Impact sound 40dB+ |
Here's your homework, and it takes ten minutes. Walk your house with this guide and write down what each floor actually needs: stairs (density), bedrooms (thickness), heated rooms (tog), hard floors (thin and firm). Then measure up — our measuring guide shows you how, or add your rooms up in a couple of minutes with the room planner on our deals page.
Bring that list to us — or read it out over the phone — and we'll match real products to it. Underlay is a place where roll ends and deals turn up too; always worth asking what's in.
A dense one, not a thick one. Look for roughly 130kg/m³ or more, or a rubber underlay, at around 8–9mm. Stairs concentrate your whole body weight onto the nose of each step thousands of times a year, and soft thick foam bottoms out exactly there. Dense underlay holds its shape over the step edge and makes the carpet last years longer in the hardest-working spot in the house.
No — density matters more than thickness. Thickness is comfort; density is performance and lifespan. Save the 10–11mm luxury underlays for bedrooms, and choose firmer, denser underlay for stairs, halls and busy living rooms.
A low-tog underlay — 1.0 tog or under — so the heat can get through. Industry guidance says carpet and underlay together shouldn't exceed about 2.5 tog over underfloor heating. A normal comfort underlay at around 3 tog will blanket the system on its own.
No. Laminate and engineered wood need a thin, firm 2–3mm underlay made for hard floors. Soft carpet underlay lets the boards flex, which breaks the click joints — and on concrete you'll also want a damp-proof membrane, which many hard-floor underlays build in.
Usually not worth it. Old underlay carries the compressed traffic pattern of the old carpet straight into the new one, and can hide damp or grit. If it's recent, quality underlay, ask us to look at it during the free measure — we'll tell you straight either way.
Free measuring across Hastings, St Leonards & Bexhill — we'll match the underlay to each room and put the whole job in writing. No pressure, no upsell.
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