The underlay you need depends on your floor type: carpet needs a thick, cushioned underlay (7–12mm, 100–140kg/m³); laminate needs a thin, firm underlay (2–3mm); LVT glue-down needs no underlay; and stair carpet needs a dedicated thin stair underlay.
Underlay for Carpet
Carpet underlay does three things: it cushions the carpet, extends its life (the carpet pile wears less when it has a soft base), and adds thermal and acoustic insulation.
For living rooms and bedrooms: choose a 10–12mm underlay with a density of 120–140kg/m³. Thicker and denser gives a more luxurious feel and protects the carpet longer.
For hallways and stairs: use a thinner, denser underlay (7–8mm, 140–160kg/m³). Thicker underlay compresses quickly under heavy foot traffic, which causes carpet to move and wear at the edges. Stairs need a dedicated stair underlay — narrower and firmer than room underlay.
For underfloor heating: use an underlay with a low tog rating (under 1.5 tog) to allow heat to pass through. A high-tog underlay will insulate against the heat you are trying to deliver into the room.
A note on felt vs foam: felt underlays (typically made from recycled fibre) are denser and more durable; foam underlays are cheaper and softer but compress faster. Felt is the better long-term choice for high-traffic rooms.
Underlay for Laminate and Click LVT
Floating laminate and click LVT need a thin, firm underlay — not the thick cushioned type used under carpet.
The role of underlay under laminate is different: it evens out minor subfloor imperfections, provides acoustic insulation (reducing the hollow click sound) and provides a small amount of thermal insulation.
Standard thickness for laminate underlay: 2–3mm. Some premium laminates come with underlay pre-attached (pre-underlay laminate) — if yours does, do not add a separate underlay layer, as too much thickness causes the floor to flex and affects the click joints.
For click LVT: most click LVT products specify a maximum underlay thickness (commonly 1.5–2mm). Exceeding this voids the product warranty. Check the manufacturer's specification before buying underlay.
Some laminates and click LVT can be fitted directly over existing underfloor heating — use an underlay rated for use with UFH and check the combined tog value stays within the heating system's tolerance.
Underlay for Engineered Wood
For floating engineered wood: similar to laminate — 2–3mm firm underlay, not the thick carpet type. Check the manufacturer's maximum underlay thickness in the installation guide.
For glue-down engineered wood: no underlay. The board is bonded directly to the subfloor with adhesive.
For glue-down LVT (Karndean, Amtico): no underlay. These products are designed to be bonded directly to a prepared, flat subfloor.
Do I Need to Buy Underlay Separately?
For carpet, laminate and floating engineered wood: yes, you need underlay. FitFloors fits underlay as part of the job — you purchase it from any retailer along with your flooring.
For glue-down LVT and glue-down engineered wood: no underlay needed or wanted.
For stair carpet: yes, but it must be specific stair underlay. FitFloors advises customers at the quote stage what to buy.
We fit any brand of underlay. If you are unsure what to buy, ask us when you get a quote — we will tell you exactly what product and thickness suits your floor and subfloor.