What’s the Best Underlay for SPC Flooring?

SPC (Stone Plastic Composite) is a rigid, waterproof bathroom vinyl flooring option with a dense stone-polymer core. While this makes it exceptionally durable, it can feel harder underfoot than softer vinyl alternatives. The right underlay helps improve comfort, reduce noise and smooth out minor subfloor imperfections without affecting the click-lock system. Choose the wrong one, and you could face joint failure, hollow spots or even a voided warranty. This guide explains the best underlay for SPC to help you get it right and achieve a smooth, consistent finish for your floor.

Do you need an underlay for SPC flooring?

It depends on the product and the subfloor. Many SPC floors come with an underlay pre-attached to the back of each plank; in this case, adding a second layer is actively discouraged and will likely void the warranty. If your SPC doesn’t have a pre-attached layer, then a thin, high-density underlay is worth using. It reduces impact noise, adds warmth, and helps compensate for minor subfloor imperfections up to around 3mm. Always check your manufacturer's guidance before buying to see whether your SPC flooring comes with underlay.

Learn more about SPC and its main properties in our guide to SPC flooring.

The best underlay for SPC flooring

Because SPC is rigid, the requirements are stricter than for laminate or LVT. The underlay needs to be thin and firm, not thick and compressible. Too much give and the click joints flex, crack, and eventually fail. Here are the most widely recommended types of underlay for SPC.

IXPE (Irradiated Cross-Linked Polyethylene) foam

IXPE is the most recommended underlay for SPC flooring and is often pre-attached to SPC planks by manufacturers. It's made from low-density polyethylene that has been cross-linked using irradiation, which produces a closed-cell foam with a consistent, stable cell structure. Unlike standard PE foam, it doesn't compress unevenly over time. It has good acoustic performance for its thickness, which sits around 1-1.5mm.

Why it suits SPC: The density is high enough to support SPC's rigid core without allowing the planks to flex. It's thin, so it doesn't raise floor height significantly or stress the locking system. The closed-cell construction also means moisture from the subfloor can't be absorbed into the material itself.

Price: Around £0.50–£1.50 per m² as a separate roll. Pre-attached versions are included in the plank cost.

Benefits:

• Excellent dimensional stability over time

• Effective sound and impact noise reduction

• Good moisture resistance without a separate DPM in many situations

• Lightweight and easy to cut and install

• Widely available

Drawbacks:

• Thinner than some alternatives, so it offers limited thermal insulation

• Not suitable as a standalone moisture barrier in wet environments

• Pre-attached versions can't be upgraded or replaced independently

EVA (Ethylene Vinyl Acetate) foam

EVA is a softer, more flexible foam material that's also frequently pre-attached to budget and mid-range SPC flooring. It's a copolymer of ethylene and vinyl acetate, which gives it slightly more elasticity and a softer cell structure compared to IXPE. It’s shock-absorbing, even though it has a lower density than IXPE, and is often between 1-2mm thick.

Why it suits SPC: EVA provides adequate cushioning and is cost-effective for lower-traffic rooms. The softer cell structure does mean slightly more compression over time than IXPE, which is worth factoring into the decision for heavy-use areas.

Price: Approximately £0.30–£1.00 per m².

Benefits:

• Lower cost than IXPE

• Good initial shock and sound absorption

• Lightweight and easy to handle

• Suitable for light-to-medium traffic areas like bedrooms

Drawbacks:

• Compresses more over time than IXPE, particularly under heavy furniture

• Less dimensionally stable in fluctuating temperature or humidity

• Not ideal for high-traffic areas or underfloor heating systems

• Weaker moisture resistance than IXPE

Combination (foam and DPM) underlay

Combination underlays come with a foam layer (usually PE or IXPE) bonded to a polythene DPM film on the underside. They're a practical choice for rooms where moisture is a concern, such as ground floors, concrete subfloors, or rooms adjacent to bathrooms. Rather than laying a separate polythene sheet before the underlay, the DPM is built in. This two-layer construction offers good acoustic absorption and comes in a thickness of around 1-2mm.

Why it suits SPC: SPC is waterproof itself, but the subfloor beneath it isn't always dry. A combination underlay removes any moisture risk from below. For bathrooms and en-suites where you're laying SPC as part of a full renovation, a combination underlay is a sensible choice.

Price: Around £1–£3 per m².

Benefits:

• Moisture protection and acoustic performance in a single product

• Saves time during installation

• Removes the need for a separate DPM sheet

• Suitable for concrete subfloors and ground-floor rooms

Drawbacks:

• The DPM film can be torn during installation if you're not careful

• Slightly thicker than single-layer foam, so check against your SPC warranty's maximum thickness allowance

• The integrated DPM cannot be repaired easily if damaged before laying

Underlay for SPC: a comparison

How thick should underlay for SPC be?

The maximum recommended underlay thickness for SPC is generally 1.5–2mm, though some manufacturers allow up to 3mm. Always check your specific product's installation guide before choosing. SPC's rigid core means there's very little tolerance for movement in the click-lock system. An underlay that’s too thick causes joints to flex under foot traffic, which leads to joint failure over time. If your SPC already has a pre-attached layer, do not add another.

Choosing the right underlay is just as important as choosing the right SPC flooring. By selecting a thin, high-density option that matches your subfloor and installation requirements, you'll improve comfort, reduce noise and protect your floor's locking system. Browse our full range of underlay to find the best option for your project.