What Is Underlay, and Does Your Floor Need It?
What underlay is, what it is made of, what it does under carpet, laminate and LVT, and when a floor needs none at all. A plain answer before you buy.
Underlay is the layer that sits between the subfloor and the floor you walk on. You never see it once the job is finished, yet it changes how the floor feels, how warm and quiet the room is, and how long the top covering lasts before it starts to look tired.
The short answer to whether you need it: almost every carpet does, most floating laminate and click floors do, and glue-down LVT and sheet vinyl usually do not, because they are bonded straight to a prepared, smooth base. The rest of this page explains why.
What underlay actually does
Under carpet, underlay takes the pressure of each footstep so the pile is not crushed against a hard floor. That is why a mid-range carpet on a good underlay often outlasts a better carpet laid on a thin or worn one. It also adds a noticeable amount of warmth and softens footfall noise for rooms below.
Under a floating floor such as laminate or click boards, the job changes. The underlay evens out very small irregularities, stops the boards rattling on the subfloor, and in many products includes a moisture barrier for concrete bases.
What underlay is made of
Fibre board feels firmer underfoot and helps bridge tiny dips in timber floors; thin foam is lighter and easier to lay but does less to hide an uneven base. Neither replaces proper subfloor preparation where a floor is genuinely out of level.
- Foam and PU (polyurethane): light, springy and the most common choice under domestic carpet
- Rubber: denser and heavier, holds up well on stairs and in busy hallways
- Felt and fibre: firm and traditional, often chosen for its stable feel
- Fibre board and thin foam sheets: made for laminate and click floors rather than carpet
When you should not use underlay
Glue-down LVT and sheet vinyl are stuck directly to a smooth screed or plywood overlay. Putting a soft layer beneath them would let the joints move and the surface dent, so the effort goes into the base instead. Some click products also come with an underlay already bonded to the back, and adding a second one can void the maker's guidance.
If your quote shows no underlay for a hard floor, that is often the correct specification rather than a corner being cut. Ask us and we will explain what sits under your chosen product.
Frequently asked questions
- Can I reuse my old carpet underlay?
- We rarely recommend it. Old underlay has already been compressed and may be crumbling, which shortens the life of the new carpet laid over it.
- Is thicker underlay always better?
- Not always. Very thick underlay can make carpet feel unstable on stairs and may reduce heat output over underfloor heating, so the right one depends on the room.
- Does laminate need its own type of underlay?
- Yes. Carpet underlay is too soft for laminate. Floating floors need a firm, thin underlay made for click boards, and many include a damp barrier.
- Does underlay help with noise in flats?
- It can. Acoustic underlays are designed to reduce impact sound for the neighbours below, and some buildings ask for a specific rating before a hard floor goes down.
Keep reading
Foam, rubber, fibre or PU underlay: which feels softest, which quietens a flat, which lasts on stairs, and which one suits underfloor heating in your home.
Why flats often need acoustic underlay for sound insulation, how ratings work, and what to check before choosing flooring.
Carpet, underlay, gripper, door bars and stairs: what each line on a carpet fitting quote covers, why stairs cost more, and where the money really goes.
How gripper-rod carpet fitting compares with fully bonded double-stick fitting, and which method suits which room or setting.
See how we survey, prepare and fit carpet across Kent.
Talk it through with a fitter, not a call centre
Tell us the floor and the room, and we will say which underlay suits it, or whether it needs one at all, when we measure up.