Compare · Polyester vs fibreglass batts · SE Queensland
Polyester vs fibreglass batts: the King of batts vs the itchy ones.
If it has to be a batt, polyester wins: non-itchy, no SDS warning, moisture-shrugging, locally made, and 20–30 years without settling. Fibreglass is cheaper, but it’s the itchy one rats love and that settles as it ages.
I fit both every week, so here’s how the two batts actually stack up: itch, the safety-sheet fine print, moisture, settling, pests and price. And one straight bit of advice: for a ceiling I’d steer you past both to pumped-in cellulose, while polyester is what I’d use under a floor.
The King of batts
white polyester, non-itch, laid wall-to-wall
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There are two batts worth talking about. One’s a lot nicer than the other.
Most people who ring me asking for “batts” picture the pink or yellow fluffy stuff. That’s fibreglass, the itchy ones. What they usually don’t know is that there’s a far nicer batt sitting right next to it on the shelf: the polyester batt, the King of batts. I fit both every week, so I don’t have a dog in the fight between them, and when I tell you the polyester is the better buy, it’s because I’ve handled and removed thousands of each over 40 years.
I hope you realise by now that you are buying a service as much as a product. The batt you pick still has to be cut to fit every bay and corner in your roof, so the install matters just as much as the brand. But between the two batts, the trade-offs are stark, and they all come back to a few things: itch and health, moisture, settling, and whether the rats want to move in.
“If you think you just must have batts, the polyester ones are the best of the batts. If batts are what you want, these are the only ones I’ll quote with a straight face.”Peter Johnson, Comfort Zone Insulation Team
The short version
Polyester is the nicer batt in almost every way that counts. Fibreglass is cheaper, and that’s about all it has going for it.
Polyester batts: non-itch, no SDS, locally made.
Polyester is the best of the batts, and I’m happy fitting them. They’re made from polyester fibre, the same family of material as a soft pillow or a fleece jacket, so there’s no glass fibre to itch, no dust to wash off your work clothes at the end of the day, and no Safety Data Sheet skin warning to worry about. They’re locally made, which keeps the money and the supply chain closer to home, and they’re pleasant to handle, which matters more than people think.
They also shrug off a bit of moisture without breaking down, which is a real advantage in our humid SE-QLD climate, and they last. In 30-odd years on the tools I’ve never seen a polyester batt settle over time. They hold their shape and their thickness, so a good polyester job should give you 20–30 years of doing its job. Under a floor, where pumped cellulose is the wrong product, polyester is exactly what I’d use.
The catch: a polyester batt is still a batt. It has to be cut into every bay and squeezed into every corner, so it still has joins and edges, and it still lets air pass through where a seamless pump-in wouldn’t. My team cuts every piece to fit so there are no gaps left, even the width of a pen, but a cut-to-fit batt always asks more of the installer than a hose does.
Fibreglass / glasswool batts: cheap, and itchy.
These are the itchy ones (Earthwool®, Gold Batts®, Pink Batts®) and they’re all fibreglass. They’re the cheapest insulation you can buy, and that’s the one thing they’ve got going for them. Fibreglass is a very cheap solution, but you really would be lucky if you’re just not buying trouble for the future. About 2% of my customers end up choosing them once they understand the trade-offs: itchy to handle, gaps from day one, settles after about ten years, and rodents love them.
They settle and break down as they age, too. I’ve removed plenty of fibreglass batts that sagged and broke down over the years, and once a batt settles or gets pushed aside, you get gaps where there used to be cover. They’re also the batt I most often find rats nesting in: the loose batts sit so lightly that mice push them up and nest underneath, leaving urine and droppings soaking into your ceiling sheets.
I’m not hiding fibreglass from you. If you decide on it after reading this, my team will still cut a piece to fit every gap. But if batts are what you want, I wouldn’t quote you fibreglass with a straight face. I’d quote you the polyester.
Read the fine print before you buy fibreglass
Their fine print tells you more than their brochure does.
Here’s the single biggest reason I steer people away from fibreglass and toward the polyester, and I want to give it to you in both halves so it’s fair. On the front of the brochure, the fibreglass batt makers market a soft, safe, comfortable product. But read the fine print: the manufacturers’ own Safety Data Sheets tell you to wear a P2 dust mask and to wash your work clothes separately from the family laundry. The fine print tells you more than the marketing brochure does. It’s telling you exactly what it is to handle. You can check it yourself on their own paperwork; for example, the Knauf Earthwool® glasswool Safety Data Sheet sets out the dust-mask and handling precautions in black and white.
Now the other half, so this stays straight. Fibreglass is a glass fibre, and the Australian Government’s CSIRO notes glass-fibre and rockwool can cause temporary skin, nose and eye irritation and that precautions should be taken when handling them. Polyester is a soft synthetic fibre with none of that glass: no SDS skin warning, no separate wash. That’s why I’d rather have my team handling it, and why your roof gets a better job out of it.
“An installer who has to wash their work clothes separately from the family laundry isn’t going to spend extra time dragging insulation into your tight corners, and that’s how gaps happen.”Peter Johnson, Comfort Zone Insulation Team
Pests & vermin
Rats love the itchy ones. Polyester’s a tougher nut, but neither deters them.
Fibreglass is the batt I pull rat nests out of week after week. The loose batts sit so lightly that mice push them up and nest underneath, and the urine and droppings soak straight into your ceiling sheets. Polyester is denser and holds together better, so it’s a tougher nut for a rat to crack and less inviting to nest in, but neither batt is treated to resist pests. With a batt you’re relying on the rodent staying away, not on the material putting it off.
That’s the real difference between a batt and pumped-in cellulose. Cellulose is treated with borax, a natural mineral salt about as toxic to you as table salt, and the insects rats feed on can’t survive in it. No insects means no food for rats, and no food for rats means no food for snakes. So if pests are your worry, no batt fixes it the way a borate-treated cellulose ceiling does. I’m so confident of that I back it with a $1,000 reward:
Side by side
Polyester vs fibreglass batts: the clean comparison.
Nine things a homeowner actually cares about. I've flagged the winner on each one, including the one axis where fibreglass wins (price to buy), and the one where they're even (a batt is a batt, so both have gaps).
| What matters | Polyester batts ★ King of batts | Fibreglass batts the itchy ones |
|---|---|---|
| Handling & itch | Polyester fibre: non-itchy and safe for your health, with no glass fibre. No dust to wash off your work clothes. better | Itchy glass fibre. The maker's own SDS tells you to wear a P2 dust mask and wash work clothes separately. |
| Safety Data Sheet | No SDS skin or dust-mask warning to wash off afterwards, locally made and pleasant to handle. better | Ships with an SDS warning; the CSIRO notes glass-fibre can cause temporary skin, nose and eye irritation. |
| Moisture | Shrugs off incidental moisture without breaking down, a real advantage in our humid climate. better | Damp and rough handling shorten its working life, and it sheds water rather than holding a leak in one spot. |
| Settling over time | In 30-odd years on the tools I've never seen a polyester batt settle. It holds its shape and thickness. better | I've removed plenty that settled and broke down as they aged, opening gaps where there used to be cover. |
| Lifespan | A good polyester batt should give you 20–30 years of doing its job without sagging. better | Often starts gapping and settling well before that, especially in tight, hot roofs. |
| Pests & vermin | Denser and holds together better, so it's less inviting, but it isn't treated to resist pests. better | Rodents love them. Mice push the loose batts up and nest underneath, leaving urine and droppings. |
| Where it's made | Locally made: the money stays closer to home, and so does the supply chain. better | Glass fibre melted in a furnace; the cheapest stock the big builders reach for. |
| Gaps (both are batts) | Still cut to fit every bay, so a batt's gaps and edges are still there. My team cuts each piece to fit. | Cut to fit too, and gaps from day one, the tight, hot corners get short-changed first. |
| Price to buy | A bit dearer than fibreglass, but for that little extra you get a far nicer, longer-lasting product. | Cheapest to buy. A very cheap solution, but you really would be lucky if you're just not buying trouble for the future. better |
That’s the scorecard. Polyester wins on every axis a homeowner cares about (itch, the safety sheet, moisture, settling, lifespan and pest-resistance) and the one thing fibreglass beats it on is the price to buy. The two are even on gaps, because a batt is a batt: both have to be cut to fit. Want all three products side by side, including the pumped-in cellulose? See the full three-way comparison table.
The straight advice
Picked your batt? Now let’s put it in the right place.
Choosing polyester over fibreglass is the easy call. The harder, more useful question is where a batt belongs at all. After 40 years and 6,000 roofs, here’s how I’d steer you, and I sell all of these, so I don’t have a dog in the fight.
For a ceiling, I’d steer you past both batts to pumped-in cellulose. A batt, even the King of batts, still gets cut into every bay and leaves gaps, and an R-rating only counts if there are no gaps. Cellulose pumps in as one seamless blanket, covers over the joists, and the borate treatment has been shown to slow flame spread, while the pests a batt does nothing to put off can’t survive in it. It’s the only product I’d put in my own mother’s ceiling.
Under a floor, it’s the opposite. Pumped cellulose is the wrong product for a crawlspace, so polyester is exactly what I’d use: hydrophobic, non-itch, and it lifts straight out if you ever need to get at the bearers. So the answer is: polyester beats fibreglass every time, but match the product to the cavity and you’ll do even better.
Straight answers
Polyester vs fibreglass batts: the questions I get asked most.
Polyester or fibreglass batts, which is better?+
If it has to be a batt, polyester wins on every count that matters to a homeowner. Polyester is the King of batts: it's non-itchy and safe to handle with no Safety Data Sheet skin warnings, it's locally made, it shrugs off incidental moisture, and in 30-odd years on the tools I've never seen one settle. Fibreglass is the itchy one, cheaper to buy, but the manufacturers' own safety sheets tell you to wear a P2 dust mask and wash your work clothes separately, rodents love nesting in it, and I've pulled out plenty that settled and broke down as they aged. The only thing fibreglass beats polyester on is the price tag. For a ceiling, though, I'd steer you past both to pumped-in cellulose.
Why are polyester batts called the King of batts?+
Because if you've decided you want batts, polyester is the best of them and I fit them every week. They're made from polyester fibre, the same family of material as a soft pillow or a fleece jacket, so there's no glass fibre to itch, no dust to wash off your work clothes, and no SDS skin warning. They're locally made, they handle moisture without breaking down, and they last 20–30 years without the settling you get from fibreglass. If batts are what you're after, these are the only ones I'll quote with a straight face.
Do rats nest in fibreglass batts more than polyester?+
Rodents will get into either batt if there's a way in, but fibreglass is the one I pull rat nests out of week after week. Loose fibreglass batts sit so lightly that mice push them up and nest underneath, and the urine and droppings soak straight into your ceiling sheets. Polyester is denser and holds together better, so it's less inviting, but neither batt is treated to resist pests the way borax-treated cellulose is. That's the difference: with a batt you're relying on the rat staying away, not on the material putting it off.
Do polyester batts last longer than fibreglass?+
In my experience, yes. I've never seen a polyester batt settle over time. They hold their shape and their thickness. Fibreglass is the opposite: I've removed plenty of fibreglass batts that settled and broke down as they aged, and once a batt sags or gets pushed aside you get gaps where there used to be cover. Polyester also doesn't mind a bit of moisture, where damp and rough handling shorten a fibreglass batt's working life. A good polyester batt should give you 20–30 years; fibreglass often starts gapping and settling well before that.
If polyester is better, why is fibreglass still everywhere?+
One reason: price. Fibreglass is the cheapest insulation you can buy, so it's what the big project builders and the lowest-bidder subbies reach for. That's the whole pitch. It's cheap. But you really would be lucky if you're just not buying trouble for the future: itchy to handle, gaps from day one, settles after about ten years, and rodents love it. For a little extra you get the polyester, which is a far nicer product to live with. Only about 2% of my own customers choose fibreglass once they understand the trade-offs.
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Thanks for reading this far. You’ve seen why the polyester is the King of batts and the fibreglass is the itchy one, what the batt makers print in their own safety sheets, and where each batt actually belongs. Whatever you decide, I’ll give you a fixed-price quote within 48 hours for most houses.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986
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