Guide · Polyester underfloor batts · Brisbane & SE Queensland
Polyester underfloor batts for a warm floor all winter.
A cold timber floor drains the warmth out of a room every winter night. We fit R3.0 polyester batts under the floor — the same rating we give a ceiling, so the boards hold the heat you’ve already paid for.
I’m Peter Johnson. I’ve been an insulation contractor in Brisbane since 1986, so a good part of forty years has been spent lying on my back under Queensland houses. This page covers why a warm floor is the whole point of underfloor insulation, why we fit R3.0 when the shops stop at R2.5, why a stapled batt barely works, and what each guarantee on the job covers. The big brands’ warranty fine print is laid out next to their headline numbers so you can see what those promises are worth.
Warm boards in winter.
R3.0 under the floor — the same rating as the ceiling
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Why insulate under the floor
Underfloor insulation in Brisbane is for warm feet in winter and a lower power bill.
A raised Queensland house has winter air moving under it all night. The boards go cold, the cold works up through your socks, and every bit of heat your living room makes drains away through the floor while your heater fights to replace it. Most people insulate the ceiling and stop — and then wonder why the house still feels cold from the knees down in July.
Fill the joist bays under the floor and the boards hold the room’s warmth instead of bleeding it. The floor stops feeling like a cold plate, the heater cycles less, and the heat you keep is heat you’re not paying to make twice. One Stanthorpe customer with timber floors wrote in their review that after we did the ceiling and underfloor, a day that dropped to 7°C outside stayed 17°C inside — their numbers from their own thermometer, and exactly the change a floor batt is for.
The rest of this page is about why the batt down there has to be polyester and why it has to hold itself up. Both of those decide whether the warm-floor part actually happens.
The R3.0 story
We fit R3.0 polyester underfloor batts under Brisbane homes because the floor matters as much as the ceiling.
The building code minimum for a floor over an open subfloor in Brisbane and the rest of SEQ is R2.0 under NCC 2022. That figure exists to get a new build approved — it’s the least insulation that lets the house pass its energy rating. Nobody sat down and decided R2.0 is what makes a floor feel warm on a July morning.
We fit the floor at R3.0, the same standard we pump a ceiling to, because in a raised house the floor is working just as hard as the ceiling at holding your warmth in. That’s my call after 6,000houses — nothing in the code makes me do it, and it’s the same call we already make on ceilings, where we install over the minimum too. You can check your own suburb’s code numbers on our R-value tool.
The part that surprises people is that you can’t buy an R3.0 underfloor batt off a shelf. Every purpose-built underfloor batt at Bunnings and from the major brands tops out at R2.5 to R2.6. R3.0 and above exists in every maker’s ceiling range and none of their floor ranges, because floor batts are milled thinner to fit the joist bays. The retail ranges stop where the code minimum is met. Ours are custom-made to get real winter comfort into a floor, and that’s the only way we know to do it.
Product ranges checked July 2026 — names and R-values drift, so check the current shelf before you rely on the table.
Underfloor batts you can buy, by R-value
| Knauf Earthwool FloorShield underfloor batt | R2.5 |
| Pink Batts HD floor batts | R2.5 |
| Bradford Optimo underfloor | R1.6 / R2.6 |
| Autex GreenStuf underfloor (polyester) | R1.5 / R1.8 |
| Expol polystyrene panels | R1.4 / R1.8 |
| Comfort Zone custom poly floor batts | R3.0 |
Zone 2 (Brisbane & SEQ) code minimum for an open subfloor is R2.0 — NCC 2022 Table 13.2.6a.
No staples, no string
Stapling squashes a floor batt flat — our poly batts hold themselves up.
A batt is mostly air. The fibre’s only job is to hold that air still, because still air is the thing that actually insulates. Squeeze the air out and you’ve squeezed the insulation out.
Now look at what a staple does. A staple is about 19mm long. Staple a soft batt up under a floor and along every fixing line you’ve pinned 90mm of fibre down to roughly 16mm of squashed material — the air is gone and that strip of batt is doing almost nothing. The makers know it, which is why their instructions have you stapling into the sidesof the joists, or stringing rope, strapping or chicken mesh under the batts instead. Side-staples still crush the edges, and anything strung under the joists leaves the batt hanging in the middle like a hammock — away from the floor it’s meant to be insulating.
That gap is the whole game. Anywhere a batt isn’t touching the floor, it isn’t insulating the floor — the heat just moves through the air gap and around it. Fibreglass is floppy, so it can’t be made to hold itself in a bay. It sags off the boards from day one (don’t even try to fix fibreglass batts under a floor). Fibreglass batts belong between the floorsof a two-storey house, lying flat on the plasterboard where gravity works for them, and that’s what most of the “floor” batts at the hardware store really are.
So we had our floor batts made stiffer, to our own spec. Under a floor everything happens above your face — you push a batt up into the bay, it presses against the joists and it holds itself there, hard against the boards, for good. Nothing to rust and nothing to work loose. We’ve fitted them that way for more than 15 years, and when the plumber needs the pipes he pulls one down, does his work and pushes it back up. I have never seen a polyester batt settle over time, but I have removed plenty of fibreglass batts that settled and broke down as they aged.
Why polyester and not fibreglass
Mop water runs straight through polyester underfloor batts.
The warmth is why you insulate the floor. Water is why the batt down there has to be polyester. You mop the floor. The kids drop a drink. The dishwasher lets go one day. Some of that water runs down through the gaps between the boards, straight onto whatever insulation is underneath — and on timber floors it happens every week of the house’s life.
Insulation that soaks water up is in trouble under a floor. A wet fibreglass batt gets heavy, the fibres mat down and the batt sags out of the joist bay. That’s not me talking — CSR’s own advice page for wet glasswool says the product has to be removed and replaced once it’s wet, because it won’t dry out in place and may never get its thickness back.
Polyester is the opposite. It’s hydrophobic — water runs through it and drips out the bottom instead of soaking in. A published comparison of insulation materials measured glass wool holding close to a tenth of its own weight in water in a very humid room while the polyester sample stayed dry. Of every batt you can buy, polyester holds the least water, and under a timber floor that’s the property that decides it.
The mop-water path is common knowledge in the trade — other insulation sellers recommend polyester under timber floors for exactly this reason: water seeps through the cracks in hardwood flooring.
The chain of events under a mopped floor
- 1Water gets through the gaps between the boards.
- 2A batt that absorbs it gets heavy and the fibres mat down.
- 3The batt sags, then drops out of the bay. The floor above it goes cold again.
- 4Polyester breaks the chain at step two — the water runs through and drips out.
The itch test
Fibreglass itch can last for days — polyester underfloor batts spare your skin.
Fibreglass itches anywhere it touches you. For some people it goes on itching for days, and a shower doesn’t wash it off. My staff use asbestos-rated masks and disposable suits any time we’re asked to install it, and we still end up itchy for about 3 days. It’s on the paperwork too — the glasswool makers’ own safety data sheets tell installers to wear a P2 dust mask, coveralls and gloves, and to wash their work clothes separately. Polyester’s sheet carries no skin warning and no dust-mask line. We’ve laid the documents out side by side on our references page.
The gear list has a gap nobody mentions. The installer suits up for one day. The national code for handling these fibres tells everyone else on a worksite to stand three metres back from the work. That works on a building site. There’s no standing three metres back for the plumber or sparky who crawls under your house next year in his work shirt, with the fibre as the thing he’s crawling through — every fibreglass batt he shifts rains loose glass on him. After forty years of watching who actually suits up under houses, I can tell you it’s the installers and nobody after them.
Dogs live under Queensland houses too. Vets have written up fibreglass doing to animals what it does to us — a vet-reviewed guide covers skin irritation from contact and real trouble if a dog chews or swallows the stuff, and Victoria’s health department lists fibreglass fibre among the hazards for anyone entering an insulated cavity. The published animal cases are mostly pets that ate it, so I’ll keep the claim modest: skin and fur take glass fibre about as well as your arms do.
“My concern is any product that irritates the skin just to touch, does not seem like it could be any good for the health of my workers.”
Two guarantees
Two guarantees cover a polyester underfloor job.
Ours covers the work. The maker's covers the batt. It pays to know which is which, so here they are side by side.
Our Best Service Guarantee →
Part 1 — ours, on the installation
- If the work's not right, you call us and we come back to fix it at no charge.
- Fixed online quote — the price we start with is the price you pay.
- Fully insured: public liability and WorkCover.
- The install is what decides whether a floor batt works, and the install is ours to stand behind.
The guarantee on the batt itself is the maker’s, and the big brands’ versions hedge theirs with rodent and maintenance clauses — the fine-print table below shows how each one words it. Our own transferable Life-of-House Guarantee belongs to the cellulose we make ourselves.
Queensland Textiles guarantee the batts for the lifetime of the building.
Part 2 — Queensland Textiles’ guarantee on the batt itself
Our floor batts are made by Queensland Textiles at Arundel on the Gold Coast, and their Certificate of Guarantee is reproduced here in full. It guarantees the material R-values — R1.5 through R3.5, which covers the R3.0 we fit under floors — for the lifetime of the building, with the R-values tested by BRANZ and the batts made to AS/NZS 4859.1 and the Building Code of Australia. The same page carries the fire test to AS/NZS 1530.3-1999 by AWTA, scored 0 for ignitability, spread of flame and heat evolved, and 0–1 for smoke.
A word on rodents before anyone reads too much into that one page. A rat chewing through a batt is damage, the same as floodwater coming through the subfloor, and it happens in your house years after the batt left the factory. No maker anywhere could reasonably cover that and none of them do — Queensland Textiles included. The big brands write the rat into a page of exclusions and Queensland Textiles kept their certificate simple instead. In practice the difference is smaller than it looks, because we went looking and could not find a single homeowner who ever had batts replaced under a maker’s product warranty — that search is in the fine-print section below.
If rodents are the worry that brought you here, the strongest answer we sell is cellulose in the roof. Our family makes it at our own factory in Tiaro. It’s a loose fill so a floor is the wrong spot for it, but in a roof it’s the one insulation going with a rodent guarantee behind it — our $1,000 Rodent Reward pays out if rodents ever nest in our cellulose.
The certificate as supplied to us — click to enlarge, or download the PDF for your records.
Reference it with the maker directly: Queensland Textiles Pty Ltd, 29 Demand Ave, Arundel Qld · (07) 5563 3090 · sales@qldtextiles.com.au · qldtextiles.com.au
Read the back page
What voids a lifetime batt warranty, brand by brand.
A warranty reads like an insurance policy. The number they want you to remember is on the cover and the conditions live in the back. The table below is the back — every point links to the maker's own document.
| Brand | The cover says | What can void or hollow it out | Terms readable before you buy? |
|---|---|---|---|
| Knauf Earthwool | “Lifetime warranty” in the resellers' marketing. Knauf's own document says 50 years. |
| ✓ Terms public Full terms are a public PDF. |
| Pink Batts (Fletcher) | “Consumer Lifetime Product Warranty” on the cover. |
| ✓ Terms public Full terms are a public PDF. |
| Bradford (CSR) | 70 years — CSR defines “the life of the home” as 70 years from install. |
| ✗ Terms unpublished Terms gated behind registration. |
| Autex GreenStuf | 50-year durability warranty. |
| ◐ Partly public Standard certificate is public; the thermal-batt version isn't. |
| Higgins Insulation | “We GUARANTEE it for the life of the building!!” — their product page, exclamation marks theirs. |
| ✗ Terms unpublished The life-of-building claim has no published terms behind it. |
| Queensland Textiles (our maker)★ The one document here with no exclusions | “All Insulation supplied by Qld Textiles is Guaranteed for the Lifetime of the Building” — their Certificate of Guarantee, shown in full in the guarantee section above. |
| ✓ Terms public The full certificate is on this page with a download link. |
Successful batt warranty claims are hard to find.
We went looking for a single documented case — on Whirlpool, ProductReview, Geekzone or anywhere else — of a batt maker actually removing old batts and installing new ones under a product warranty. We found none. The closest thing is a forum thread of homeowners wondering whether sagging would even count as a defect. The paperwork explains why: Pink Batts’ own Australian warranty document excludes the cost of removal and re-installation in writing, so even a fully successful claim buys replacement material at the depot — the labour, which is most of the real cost of a ceiling or floor job, stays yours.
Buy the batts at the hardware shop and install them yourself and the odds get longer again. Every warranty above only stands while the batts were properly installed to the maker’s instructions, and proving that is on you, not them. Knauf’s own claim conditions go a step further and ask for a receipt with the seller’s and the installer’s details on it (their clause 3A). A professional job comes with a dated job file and photos to point to. A DIY job has a folded instruction sheet from the packet.
Keeping a batt warranty alive costs money every year.
Every big-brand warranty above leans on words like neglect and proper maintenance, and a rat-chewed batt gets argued as your failure to maintain the house. To hold the paperwork that wins that argument you’re paying for it — pest control runs $150 to $400 a visit, rodent treatment $200 to $550 and a termite inspection $200 to $400 a year. Call it $300 to $800 a year to stay on the right side of a warranty that looked free on the cover.
Ours takes one sentence. If something’s not right with the work, call us and we come back.
Where batts really end up
What “recycled” really means on an insulation bag.
New polyester batts really are spun from recycled bottles.
The fibre in our floor batts is spun from virgin and recycled polyester, and old PET drink bottles are one of the inputs — that’s the maker’s own description, and their data sheet also lists the finished batt as recyclable. Those are the claims their own paperwork supports, so those are the claims you get.
Used batts out of a roof or floor go to landfill — ours, theirs, everyone’s.
Old batts pulled out of a roof or floor are a different thing entirely. We could not find a single facility in Brisbane or anywhere in Queensland that takes used insulation batts for recycling. Even clean polyester batts out of an office strip-out get knocked back by the manufacturers. Used batts covered in roof dust and rat droppings go to landfill. Any company implying otherwise should name the facility.
Ask for the percentage behind a fibreglass “recycled” label.
The big glasswool brands print “up to 80% recycled glass” on their marketing. Up to is doing the heavy lifting in that sentence. When Knauf’s American arm had its number independently checked, the validated post-consumer figure was 55.7%.
The next bit surprises people. There is no law in Australia setting a minimum recycled content before a maker can print the word recycled on the bag. The ACCC’s green-marketing guide polices how the claim is worded, and stays silent on how big the number has to be. A batt with a sliver of recycled material in it can wear the word legally. So when you see “recycled” on a bag, ask for the percentage — and ask who checked it.
Who makes them
Queensland Textiles build our poly floor batts to our spec.
Our floor batts come from Queensland Textiles, an owner-run manufacturer at Arundel on the Gold Coast — the sort of outfit where the bloke whose name is on the paperwork still answers the phone. Being local helps when I need floor batts, because they make the batts stiffer as a special order just for Comfort Zone Insulation — a batt that holds itself between the joists at R3.0. They’ve built it that way for more than 15 years.
You don’t get that from the big end of town — the biggest batt brand in the country is now owned by a French multinational. Try ringing them and asking for a stiffer batt.
Tamborine — a batt made to our spec holding itself between the joists. Nothing else is holding it up there.
Under real floors
Polyester underfloor batts under real Queensland houses.
Photos and videos from our own jobs — filmed and shot under the houses, not in a studio.
What customers say
Reviews from Queensland underfloor insulation jobs.
Written reviews, filmed customer stories and the profiles where you can read every one — then a spot to add your own.
Did we do your underfloor? Leave us a review.
A quick honest review genuinely helps a small family business, and helps the next person decide. Thank you.
Common questions
Polyester underfloor batt questions, answered.
What R-value do I need for underfloor insulation in Queensland?+
The building code minimum for a floor over an open subfloor in Brisbane and SEQ (climate zone 2) is R2.0. That number gets a new build approved. We fit R3.0 under the floor — the same standard we give a ceiling — because in a raised house the floor is losing your warmth all winter and the code minimum was never set as a comfort target.
Why can't I buy R3.0 underfloor batts at Bunnings?+
The dedicated underfloor batts at retail top out at R2.5 — Earthwool FloorShield and Pink Batts HD floor batts are both R2.5, Bradford Optimo runs R1.6 and R2.6, and Autex's underfloor poly runs R1.5 and R1.8. Underfloor batts are milled thinner to fit joist bays, so the ranges stop where the code minimum is met. Getting R3.0 into a floor takes a denser batt, and that's why ours are custom-made rather than picked off a shelf.
How do polyester underfloor batts stay up without staples?+
They're made stiffer than a normal batt, to our spec. You push one up between the joists and it presses against the timber and stays there. Stapling is the alternative and it wrecks the batt — a staple pins the fibre down to roughly its own length, about 19mm, and the squashed strip holds almost no air. Air is the thing that insulates. That's why the makers staple to the sides or string rope and mesh under the joists instead, and why those batts end up sagging away from the floor.
Are polyester underfloor batts itchy to handle?+
There's no glass in the fibre, so there's nothing to bite your skin. Polyester is the same fibre that's in your doona and your pillows, and I normally rub a batt on my face just to prove how non-itchy it is. Fibreglass itches anywhere it touches you and for some people it keeps itching for days — a shower doesn't wash it off. Polyester you can handle bare-handed all day.
Will mopping the floor wreck the insulation underneath?+
Not with polyester. Mop water that gets through the gaps in the boards passes straight through the batt and drips out. Fibreglass soaks it up instead. A wet fibreglass batt gets heavy, mats down and ends up hanging out of the joist bay — and CSR's own advice for wet glasswool is that it has to be removed and replaced because it won't dry out in place.
What guarantee do I get with polyester underfloor batts?+
Two. Our Best Service Guarantee covers the installation — if the work's not right, you call us and we come back to fix it at no charge. The batt itself carries Queensland Textiles' Certificate of Guarantee — the material R-values, tested by BRANZ, guaranteed for the lifetime of the building. The full certificate is shown on this page with a download link.
Do rats or termites eat polyester underfloor batts?+
There's nothing in polyester for them to eat — it's not paper or timber, and Queensland Textiles' own data sheet lists the batts as vermin and rot resistant. A determined mouse can still nest in nearly any soft material, and worth knowing: a rat-chewed batt is exactly the claim the big brands' warranties knock back as poor maintenance. We also fit batts clear of the perimeter so your pest inspector can still read the framing.
Are polyester batts better than fibreglass under a floor?+
Under a floor, yes. Polyester holds the least water of any batt, stays up in the bay without fixings and sheds no glass on the next tradie under there. Fibreglass is floppy — it sags away from the boards, and anywhere a batt isn't touching the floor it isn't insulating it. Fibreglass batts belong between the floors of a two-storey house, lying flat on plasterboard. The full head-to-head is on our comparison page.
Can I install polyester underfloor batts myself?+
The material won't stop you — no gloves, no mask, no itch. The crawlspace is the hard part: tight access, low clearance, and every batt pushed home above your face with no gaps. Check what you're buying too, because most floor batts at the hardware store are really between-floor batts made to lie flat on a ceiling, and they won't hold themselves up under a floor.
Get a fixed home insulation quote for polyester underfloor batts in Brisbane.
Send me your address and I’ll work out a fixed home insulation quote for your underfloor — usually within 48 hours and no deposit. If your floor isn’t worth doing I’ll tell you that too. We insulate homes across Brisbane & SE QLD.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986