Short answer: most hybrid planks sold in Australia already have an underlay bonded to the back of the board, so you don’t need to lay a separate one. The exceptions are acoustic upgrades for apartments, moisture protection over a concrete slab that hasn’t been sealed, and self-levelling work where the existing subfloor is out of tolerance. Here’s how to tell which category your job falls into.
Why hybrid usually doesn’t need a separate underlay
Almost every hybrid plank we stock — Easi-Plank, Embelton, Aqua Stone and the rest of the SPC and RCB ranges — comes with an IXPE or EVA acoustic pad already laminated to the underside of the board. The pad is typically 1-1.5 mm thick. It softens the step, knocks down the hollow click sound that bare SPC makes on a slab, and gives the click joint something to settle onto.
If you lay a second foam underlay underneath a plank that already has IXPE attached, you’ll usually void the manufacturer warranty. Stacking underlays makes the system too soft, which lets the click joints flex and eventually pop apart under furniture loads. Check the back of the plank or the spec sheet — if you can see a grey, black or white foam layer bonded to the SPC core, you’re done.
When you do still need underlay
Upstairs apartments and acoustic compliance
If you’re laying hybrid in a strata building, the body corporate will usually specify a minimum acoustic rating — commonly an LnTw or impact-noise figure that the floor system has to meet end-to-end. The 1-1.5 mm IXPE on the back of the plank doesn’t always hit that number on its own. In that case you do lay a dedicated acoustic underlay underneath the plank, but it has to be one the manufacturer has tested with their product. Lay the wrong density and the click joints still flex.
Concrete slabs and moisture
Hybrid is waterproof from above, but a green or unsealed concrete slab can wick moisture up from below. New slabs need to be tested for residual moisture before any flooring goes down — most manufacturers ask for a reading under 75% RH or 4.5% MC. If the slab reads high, you don’t need a foam underlay; you need a moisture barrier (a builder’s-grade poly sheet, typically 200 micron, taped at the joins) laid before the planks. That’s a different product to acoustic underlay and it sits underneath the IXPE.
Uneven subfloors
If your subfloor is out by more than 3 mm over a 2 m span, no underlay will save you. The fix is self-levelling compound poured before the planks go down, not a thicker foam. SPC is rigid, so a high spot in the slab telegraphs straight through to the surface and the click joints crack apart over time. We see this most often in older homes where the slab has settled, or in renovations where tiles have been removed and the bedding is left uneven.
Underfloor heating and other edge cases
Some hybrid ranges are rated for use over hydronic or electric underfloor heating up to a maximum surface temperature (commonly 27 degrees C). Check the spec sheet — if the range is approved, you generally lay it directly over the heating system without an additional underlay, since the IXPE pad is already factored into the heat-transfer calculation. Adding extra foam underneath insulates the plank from the heat source and you’ll lose performance.
How this compares to vinyl planks
Loose-lay and glue-down vinyl is a different conversation — most of those products don’t have integrated underlay, and the underlay rules change accordingly. We’ve covered that separately in do you need underlay for vinyl flooring. The split between SPC and RCB hybrid construction also affects how the floor handles imperfect subfloors, and we’ve broken that down in our SPC vs RCB guide.
The practical checklist
- Check the back of the plank — if there’s foam already bonded on, don’t add another underlay.
- Read the manufacturer’s installation guide before you buy. The warranty terms are explicit about what underlay is and isn’t allowed.
- Test the slab for moisture before install. Add a poly moisture barrier if it reads high.
- Self-level any subfloor undulation greater than 3 mm over 2 m before the planks go down.
- For apartments, get the body-corporate acoustic spec in writing and match the underlay system to it.
If you’re still pricing the job, our hybrid flooring cost guide covers underlay, levelling and labour line items, and the best hybrid flooring brands in Australia guide covers which ranges ship with which underlay spec. We carry these ranges across our Sydney and Brisbane showrooms — happy to talk through your subfloor and acoustic requirements before you order.