Acoustic underlay for hybrid flooring: getting the layers right

A second layer of underlay can seem like an easy way to make a hybrid floor quieter. Before adding anything, check the board’s installation guide.

Many hybrid floors already have a backing attached. Their locking joints depend on the support beneath them, so the maker’s permitted construction matters as much as the acoustic figure. This guide focuses on that compatibility question; laminate has its own underlay guide.

Does hybrid flooring need a separate acoustic underlay?

Usually not, and adding one can void your warranty. Here is what five installation guides say.

Sources: Preference Floors guide, Signature Floors guide, Karndean guide, Godfrey Hirst instructions and Quick-Step instructions.

The pattern is clear. Do not double an attached pad with a separate underlay unless the plank maker allows it in writing. Where a maker does allow extra, it wants something thin and dense, not soft. Signature’s guide gives the reason: “Soft underlayment and soft substrates will diminish the products inherent strength in resisting indentations & lock integrity.”

How much quieter does an IXPE underlay make a floor?

IXPE is a cross-linked polyethylene foam, sold both as attached pads and as separate rolls for floating floors. Three published documents give numbers for it, and they measure different things.

Laboratory, separate IXPE roll. CSIRO tested 14 mm engineered boards floating on a 2 mm IXPE roll, loose laid with taped joins, on a bare 150 mm concrete slab with no ceiling. The result was Ln,w 61 dB and an improvement of ΔLw 18 dB (CSIRO report INR289-16-1, 2024). The same report shows where the improvement happens: about 3 dB at 100 Hz, but 19 dB at 1,000 Hz and 38 dB at 2,000 Hz. A thin foam cuts the click of heels far more than the thud of feet.

Laboratory figures on a plank with a pad. Karndean’s data sheet for its 5.5 mm Van Gogh Rigid Core lists ΔLw 21 dB (EN ISO 10140-1) and Ln,w 56 dB, and says it suits upper floors of apartments “without the need for a separate acoustic underlay” (Karndean data sheet, October 2025). The sheet does not name the slab or the laboratory, so ask for the full report.

On site, separate IXPE roll. An acoustic consultant tested a 2 mm IXPE roll under 8 to 15 mm laminate, engineered and bamboo floors in a Sydney apartment. The slab was about 200 mm with a plasterboard ceiling below. Results were L’nT,w 41 to 43, but the bare slab with that ceiling already measured 55 (Koikas Acoustics certificate, 2022). The report adds that it tested a 1 m² sample and that a floor laid wall to wall can rate up to 3 points worse.

Read those together and the lesson is simple. A laboratory ΔLw tells you how much an underlay improves a standard slab. The number in your by-law is measured in your building, with your slab and your ceiling. Our acoustic ratings guide explains the difference in full.

Attached IXPE, separate foam or rubber: which suits a floating floor?

The rubber figure comes from REGUPOL test RG090, laid loose. A 5 mm rubber mat and a 2 mm foam land within a decibel of each other here. Different boards were used, so this is not a head-to-head test, but thickness alone clearly does not rank underlays.

What if you are considering laminate or vinyl plank?

Laminate is a floating floor like hybrid, but most laminate has no attached pad, so an underlay is part of the system. Quick-Step’s instructions say “Underlay is essential for all laminate installations”, ask you to tape the joins with the underlay’s built-in tape, and say any alternative must meet all the performance criteria of its approved underlays.

Thin vinyl plank that is glued down is a different system again. REGUPOL tested 2 mm vinyl planks bonded to its 3 mm sonus multi sheet, bonded to a 150 mm slab, and measured Ln,w 58 dB and ΔLw 18 dB (REGUPOL test RG019). If your vinyl plank clicks together and floats, treat it like hybrid and follow the plank maker’s guide.

Is QEP Acoustic Pro or a Bunnings underlay a good choice?

Bunnings lists the QEP 2 mm IXPE Acoustic Pro underlay for floating floors online, as at September 2026. We looked for a published acoustic test report for it and did not find one we could open, so we cannot give you a figure. That is not a judgement on the product. It means you should ask the seller for the test report before you rely on it.

Two checks matter more than the brand. Does your plank already have a pad? If so, the makers above say do not add a roll. And does the report show a laboratory ΔLw with the standard, the lab and the full build-up? “Independently tested” without the report is not evidence a committee can use.

Do you need a moisture barrier on a concrete slab?

Yes, in most cases. Hybrid planks are waterproof on top, but the makers are clear that the plank is not a moisture barrier. Preference Floors says its attached underlay “does not contain a PE moisture barrier film”, so you must lay 200 µm polyethylene film over all subfloors and tape the joins. Godfrey Hirst asks for a moisture test to AS 1884 (concrete below 80% RH) and, where no test is done, a 200 micron plastic sheet overlapped and taped, or a liquid membrane. Karndean sets its own limit of 95% RH and asks for a damp proof membrane above it. Follow the plank maker’s figure, because the limits differ.

How do you install a floating floor over acoustic underlay?

1. Read the plank maker's guide

   Check for an attached pad, whether extra underlay is allowed, and the moisture limit.

2. Test the slab and lay the film

   Test moisture as the guide requires, then lay the specified film with taped joins.

3. Lay any separate underlay loose

   Roll it out a row at a time and tape every join. Do not glue it unless both makers say so.

4. Keep the floor off the walls

   Use the expansion and perimeter detail specified for the exact floor, room layout and climate; dimensions differ between products. Do not improvise a sealant detail. The ATFA warns a floor hard against a wall carries noise into the next unit.

5. Never fix through the floor

   Godfrey Hirst warns that door stops and tracks pin a floating floor. A fixing through an underlay also bridges it.

6. Check doors and stairs

   Quick-Step says to check doors still open afterwards. On stairs, Signature glues planks with the pad removed, and Preference notes the nosing has no underlay.

The advice against bridging comes from the ABCB handbook, which warns that nails and screws through a resilient underlay “diminish its performance”. The perimeter advice is from the ATFA information sheet on installing over acoustic underlays.

What voids a hybrid flooring warranty?

From the guides above: adding an underlay the maker does not allow, using soft foam under the plank, using an underlay thicker than the maker’s limit, skipping the moisture film or moisture test, filling expansion gaps with sealant, and fixing anything through the floor. Preference Floors adds that without site records and photos of your moisture tests there is no product warranty. Keep those records.

What to check on the data sheet

• Does the plank already have an attached pad, and what does the plank maker allow under it?
• Is there a laboratory ΔLw and Ln,w, with the test standard (ISO 10140-3 and ISO 717-2, or older ISO 140-8) and the lab named?
• Does the report list the full build-up: plank, underlay, thickness, slab thickness and any ceiling?
• Was it floating or glued, and how big was the test sample?
• What are the density and thickness, and is it rigid enough for the plank maker's rules?
• Does it include a moisture film, and what thickness?
• Is there an on-site L'nT,w result from a building like yours?
• What do the plank and underlay warranties say about using them together?

For the planks themselves, including 6.5 mm and 9.5 mm cores and star claims, read our guide to acoustic hybrid flooring. For how underlay works across every floor type, go back to the acoustic underlay hub.

For a laminate installation, use the dedicated laminate underlay guide. For the perimeter detail, read floating-floor expansion gaps before the trims go on.

For a laminate installation, use the dedicated laminate underlay guide. Read about floating-floor expansion gaps before the trims go on.