Guide · Insulation particle size & health · Brisbane insulation contractor since 1986
Are fibreglass batts safe? What the manufacturers’ own documents say.
Should I pull out the fibreglass batts my builder put in — or are they safe to leave up there? That is the question I get asked in a hundred different wordings. The answer starts with the size of the fibre. The industry’s own national code puts 10 to 20 per cent of glasswool fibre under 3 microns across, fine enough to be breathed deep into a lung and far too fine for your eye to pick up. NOHSC:2006(1990), Schedule 3 (Glasswool) §7, printed p.42 (PDF p.50) — “in the order of 10 to 20 per cent” ↗ That code wrote the figure for the coarser 5 to 8 micron glasswool of 1990. Knauf’s current Australian safety data sheet has the fibre finer again at 3 to 5 microns. Knauf Insulation AU/NZ SDS KI_DP_101, rev 3.0, 30/07/2020, section 9, p.7 — “Nominal diameter of fibres 3 - 5 μm” ↗ A finer fibre puts more of itself under that 3-micron line rather than less. That is the whole argument on this page, out of the industry’s own paperwork.
I’m Peter Johnson. I’ve been a home insulation contractor since 1986 and I’ve had my hands in fibreglass, polyester and Cellulose Fibre Insulation across more than 6,000 Queensland homes in Brisbane and SE Queensland, so most of what’s on this page I learned off my own arms first and then went looking for the paperwork to see whether the paperwork agreed with me. It does. Nearly every number below comes out of the glasswool industry’s own documents rather than mine.
An Ipswich roof I opened up. The batts are old yellow glasswool gone grey with years of dust, pulled apart at the joins, with the timber showing through. Every trade that has been up here since it was laid has moved one of those. Every move puts fibre in the air.
3 microns is the number that matters.
The code puts 10 to 20% of glasswool fibre at or under it
Why I built this page
Batt companies scare people about cellulose fibre being loose in your roof — but the loose, respirable fibres in batts are substantially more than Cellulose Fibre Insulation at just 0.1%.
I’m not a scientist. I’m a Brisbane insulation contractor who has had fibreglass, polyester and Cellulose Fibre Insulation in his hands since 1986. This page is one narrow argument I have watched play out across six thousand roofs: the size of the particle a product sheds decides where that particle ends up. A batt sheds a far finer particle than plant fibre does. Most of the dust off a batt is too fine to see once it is kicked up and blowing around, which is exactly why I want the numbers written down with the documents beside them.
Cellulose Fibre Insulation, which some people call Modern Plant Fibre Insulation, is a heavier and much coarser fibre made out of recycled paper. When the NIH generated the dust off real cellulose blowing work, under 0.1% of it was even small enough to breathe deep in. The fraction that was held no cellulose material in it at all — it was fire retardant and trace clay. NTP TOX-74, plain-language summary p.5 — “less than 0.1% were of the size that were respirable by the lung” ↗ Glasswool batts sit at the other end of the same scale: the industry’s own 1990 national code puts 10 to 20% of the fibre under that same 3-micron respirable cut. NOHSC:2006(1990), Schedule 3 §7 — “in the order of 10 to 20 per cent” ↗ I have worked out the full kilogram-by-kilogram exposure arithmetic on its own page — how much fibreglass dust ends up in your house. This page is the safety question underneath that number.
- Fine particles are the ones that travel and the ones you cannot see, so the size of the fibre decides where it ends up.
- A batt sheds a 2 to 8 micron glass filament. Plant fibre sheds a coarse fibre that drops where it is put.
- Every figure on this page has the document it came from linked directly beside it.
- Do you have fibreglass batts in your roof now? We can quote to take them out or to pump Cellulose Fibre Insulation over the top, so what is above your ceiling sheds under 0.1% respirable dust instead of the 10 to 20 per cent the code puts under 3 microns.
The definition everybody trips over
What does “respirable fibre” actually mean? And why is it thinner than 3 microns and longer than 5 microns at the same time?
A fibre is a needle, not a grain of sand, so it has two measurements. The definition uses both of them for two different reasons.
Thinner than 3 µm across
That is the width. It’s thin enough that it rides the air straight past your nose and your throat instead of being caught on the way through and settles right down in the bottom of the lung.
Longer than 5 µm end to end
That is the length. Long enough that the cleaning cells in your lung cannot get all the way around it and carry it back out the way a short particle gets carried out.
Put the two together and that is the shape the definition is really describing — a long thin splinter, thin enough to get all the way in and long enough to be hard to get back out. That is why a product’s average diameter on its own never tells you the whole story: what matters is what share of the fibre sits under the width cut.
For scale, the code itself says a strand of human hair is approximately 50 micrometres in diameter, so a 3-micron fibre is about a seventeenth the width of a hair off your own head. NOHSC:2006(1990), definitions cl 4.1, printed p.12 (PDF p.20) — “A strand of human hair is approximately 50 µm in diameter” ↗ You cannot see one.
The centrepiece of this page
Insulation fibre size compared, ranked worst to best on dust: how thick the fibre is, how much of it is respirable, and how long it hangs in the air.
Every cell either carries the document it came from directly beside it or says “not established”. Nothing here has been filled in by guessing. Where a number is my own arithmetic rather than a quoted figure I have said so on the row. Loose-pumped fibreglass sits third, below the two bound-batt rows and above Cellulose Fibre Insulation and polyester: I can source its fibre diameter but nobody has published what share of it is respirable — see the measured comparison directly under the table for why it still belongs up near the top rather than being left off altogether.
| Material | Fibre diameter | Share under 3 µm — the respirable size | Time to fall 1 m in still air | Peter’s rating on dust |
|---|---|---|---|---|
Rockwool batts Spun off molten rock rather than molten glass. Same family of fibre — the code gives it its own schedule. | 5 to 8 µm | 15 to 25% of that fibre is under 3 µm respirable size — the biggest measured share of any product in this table. Same code, Schedule 1 §7, printed p.26 (PDF p.34) — “in the order of 15-25 per cent” ↗ | About 9 to 22 minutes My own arithmetic off the sourced fibre size. | Biggest share under 3 µm |
Fibreglass batts (glasswool) The pink and yellow and brown batts in nearly every Queensland ceiling. Bound with a resin so the fibre holds together until somebody moves it. | 5 to 8 µm in the 1990 code, 3 to 5 µm in Knauf's current Australian sheet | 10 to 20% of that fibre is under 3 µm respirable size, small enough to be breathed deep into your lungs. | About 9 minutes at 8 µm, about an hour at 3 µm The 3 µm figure is my own arithmetic, the 10 µm anchor is sourced. | Bound, until it isn't |
Listed for fibre diameter only — not rated Loose-pumped fibreglass (like Knauf Jetmax) A different fibreglass product, pumped loose through a blowing machine rather than laid as a batt — not the same product as pumped-in Cellulose Fibre Insulation. Knauf's own datasheet for its Jet Stream MAX product describes it as unbonded, meaning no resin holds the fibre together at all. | 2 to 5 µm | Not established — no research published on this specific category's respirable share. The only real physical difference from a bound batt is that this category has no binder holding the fibre together, which points toward more airborne dust rather than less. See the measured batt-vs-loose-fibreglass comparison directly below the table ↓. | About 20 minutes to over 2 hours My own arithmetic off the diameter range. | No rating Not rated |
Polyester batts The same fibre that is in your pillow. I rub a batt of it on my own face in front of customers to show them there is nothing in it to itch. | 8 to 40 µm | Stated as none. The manufacturer's own sheet says any free fibres are not of respirable size. Same Autex MSDS — “any free fibres which may be present are not of respirable size” ↗ | About 20 seconds to 9 minutes My own arithmetic off the sourced fibre size. It drops while you watch. | No respirator asked for |
✓ Cellulose Fibre Insulation Modern Plant Fibre Insulation. Recycled paper fibre treated with borate, boric acid and borax, made by us at our own factory in Tiaro. Get a quote for Cellulose Fibre Insulation → | No spun filament diameter — it is shredded plant fibre, not a manufactured thread | Under 0.1% of the dust generated is respirable size. The NIH found that fraction held no cellulose material in it. Measured on four American products. | Not established Nobody has published a still-air fall time for a cellulose fibre. The trace under-0.1% fraction has a mean equivalent diameter of 0.6 to 0.7 µm and is fire retardant and clay, not fibre (NTP TOX-74, Results — “ranged from 0.6 to 0.7 µm”). | Least respirable dust |
Blowing loose fibreglass measured a long way dustier than laying fibreglass batts
Some companies in Brisbane sell blow-in fibreglass — please don’t confuse it with our Modern Plant Fibre Insulation, which is far less dusty, less respirable and safer than any fibreglass product.
A field survey monitored insulation installers in 107 houses across 11 US states and counted respirable fibres in the air. Laying glasswool batts averaged 0.14 fibres per cubic centimetre. Pumping loose fibreglass that had a binder in it averaged 0.55 for the installer — roughly four times higher, both figures measured on fibreglass. Loose fibreglass with no binder at all ran highest of the lot, averaging 7.67, over fifty times the batt figure. Lees et al. 1993, Applied Occupational and Environmental Hygiene 8(12):1022–1030, quoted in the NTP Report on Carcinogens glass wool profile, Exposure section ↗
That 1993 study measured the category, not any single modern product, so the 7.67 figure describes 1990s unbonded loose-fill fibre in general rather than any current brand. Knauf’s own product datasheet for Jet Stream MAX describes it as an unbonded glasswool insulation. Knauf Insulation, Jet Stream MAX (Ceiling) product datasheet — “an unbonded, glasswool insulation” ↗ Unbonded sits closer to the “no binder” end of that study than the “with binder” end, which is why the loose-pumped fibreglass row in the table above stays unrated rather than borrowing the 0.55 figure — that number belongs to a bonded loose-fill product, not an unbonded one.
I have the full kilogram-by-kilogram breakdown of what any of these figures mean for a real Brisbane roof on a separate page — how much fibreglass dust ends up in your house.
Watch the loose fibres come off a batt the moment it’s moved — filmed on a real job, not staged.
Loose fibres floating in the air off a fibreglass batt
Loose fibreglass fibres you can actually see floating in the air the moment a batt gets moved.
Read the transcript
Just pulling out this little bit of fibreglass that somebody hung in here and then decided it was too itchy to insulate their floor with and too hard to get it to hold up. I'm installing this polyester batt and it's quite easy to put in place for a professional installer. But have a look at all of this because you've got to wear really good safety equipment when you use fibreglass because have a look at all the fibres that come out of here. You see that? Yep, all of that fibreglass is itchy. And people say, well why would I bother paying more for the same R value as polyester? You don't have to have this stuff in your home, that's why. I'm not going to touch it any more than that.
This is fibreglass, not our Modern Plant Fibre Insulation. It is here to show what fibre actually does when a batt gets disturbed, on camera rather than in a paragraph.
The thing that made me go and read a patent
Their own patent shows fibreglass still itches — the new fibre only scored about half the old prickle number, not zero.
Anybody who handled fibreglass twenty years ago and handles it now will tell you the new stuff is nothing like as savage on your arms. The industry has every right to be proud of that. What I wanted to know was how they did it — there are only two ways to make a fibre stop poking you: change what it is made of or make it thinner. They did both, for two different reasons. Only one of them helps your lungs.
The itch part is thinner fibre, straight out of Owens Corning’s own patent. It says conventional residential fibreglass insulation products have fibre diameters typically greater than 4 microns and that their new product runs 2.03 to 3.04 microns. Then it measures the itch properly, using the international wool industry’s own prickle standard on a Wool Comfort Meter — the same test that tells you whether a jumper will scratch. The old specimens scored between 150 and 267. The new fine-fibre ones still scored between 57 and 140. Owens Corning patent US 12,297,342 B2, “Fiberglass insulation product”, granted 13 May 2025 — Table 6 (Comfort Factor 267, 243, 170, 192, 150 for prior-art specimens A1–A5; 131, 74, 75, 57, 140 for specimens B1–B5) and FIG. 3 ↗ The same invention filed in Canada as CA3102002A1, if you want the family ↗ Marketed as low-irritant, that description only holds up against the old, itchier fibreglass. It is not low against polyester, which the manufacturer’s own sheet says sheds no respirable fibre at all. It is not low against Cellulose Fibre Insulation either.
Thinner fibres go deeper into your lungs — that is the definition of the problem
The US government’s own carcinogen profile puts it in one line: fibre aerodynamic diameter determines whether a fibre will be deposited in the lungs or the upper airways, and thinner fibres will be deposited into the deep lung. NTP Report on Carcinogens, 15th ed., glass wool profile, Fiber Properties section, p.3 ↗
The same profile cites work finding that operations making smaller-diameter fibre put airborne fibre concentrations many orders of magnitude higher into the air than larger-diameter operations, with more of the fibres of respirable size. Same profile, Exposure section, p.6, citing Dement 1975 ↗ Handling a finer product does not just put proportionally the same cloud into the air — it puts a finer cloud into the air. That means more of it can be inhaled deep into your lungs when you use batts like this in your home.
The question I get asked most on site
Fibreglass is essentially glass. Glass is silica. Is it the same silica that causes silicosis?
Every stonemason and every benchtop bloke in Queensland has heard about silicosis by now, so as soon as I say fibreglass is basically glass and glass is silica, somebody puts the two together and asks me straight out. The answer is no. It is the same chemistry in a different physical form — the form is the entire ballgame.
Crystalline silica — the one that causes silicosis
Quartz dust, released when somebody cuts, grinds, drills, polishes or crushes stone, concrete or engineered stone. The molecules sit in a rigid repeating pattern. That is what causes silicosis and it is irreversible. IARC’s wording is that crystalline silica inhaled as quartz or cristobalite from occupational sources is Group 1, carcinogenic to humans. IARC Monographs Vol. 68 (1997), Silica, §5.5 Evaluation — “inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1)” ↗
Amorphous silica — the structure glasswool has
Sand and recycled glass melted at 1,300 to 1,500 °C and spun out into fibre. Melting scrambles the order, so the molecules sit in no pattern at all — an amorphous structure. ATSDR Toxicological Profile for Synthetic Vitreous Fibers, Sept 2004, §1.1, p.1 — “The randomly oriented molecular structure of synthetic vitreous fibres is called an amorphous structure” ↗ IARC does rate amorphous silica Group 3, not classifiable. That rating belongs to a different set of materials than the one in your roof — the agents named under that heading are fumed and precipitated silica, silica gel, diatomaceous earth and vitreous silica. IARC Monographs Vol. 68 (1997), Silica, agents evaluated — “Amorphous silica: pyrogenic (fumed) amorphous silica … precipitated silica; silica gel … diatomaceous earth … vitreous silica” ↗ Glasswool got its own IARC evaluation. It landed in the same Group 3. IARC Monographs Vol. 81 (2002), Man-made Vitreous Fibres — “Insulation glass wool … not classifiable as to their carcinogenicity to humans (Group 3)” ↗
The glasswool manufacturer’s own composition sheet lists the fibre as amorphous, non-crystalline, at over 85% of the product by weight. The remaining share on that same sheet is an organic binder — a resin — not a crystalline fraction of the glass. There is no crystalline silica ingredient listed on either major manufacturer’s SDS I checked. Crystalline silica can form inside vitreous mineral wool through devitrification, but only at sustained temperatures above roughly 1,000°C, documented for high-temperature industrial insulation wools, not for standard batts in a Queensland roof. CSR Bradford SUIS, FBS-1 Glasswool, §3 Composition, p.2 ↗
And the amorphous structure itself is not the reason glasswool sits at a lower rating. The Australian government’s own comparative toxicology review reports a 13-week inhalation study in rats where crystalline silica at 3 mg per cubic metre significantly raised the mutation frequency in lung cells, while amorphous silica showed no such rise even at 50 mg per cubic metre, nearly seventeen times that dose. NICNAS/AICIS, Crystalline silica: Human health tier II assessment, 2018, p.8, citing Government of Canada 2013 — HPRT assay in rat alveolar epithelial cells, 13-week inhalation ↗ That is an animal study rather than human data. It is a measured difference in what the two forms actually do rather than an absence of testing on the amorphous one.
One nuance their own regulator won't let me skip
The US National Toxicology Program does list certain glass wool fibres as reasonably anticipated to be human carcinogens — but that finding is scoped to fibres that are biopersistent, meaning long, thin and slow to dissolve in lung fluid, which is a question of fibre shape and durability, not of amorphous structure. The same profile separately confirms that standard insulation-grade glasswool is the low-biopersistence, more biosoluble category, which is the category that carries the weaker signal. NTP Report on Carcinogens, 15th ed., Certain Glass Wool Fibers (Inhalable), pp.1, 3 ↗
Fibreglass and silicosis: the line I'll put my name to
Fibreglass not causing silicosis does not make fibreglass harmless. The same CSR Bradford document that confirms the fibre is amorphous also says unprotected exposure to high levels of dust during installation or removal may cause discomfort of the nose, throat, and upper and lower respiratory tract, especially in people with hay fever, asthma or bronchitis — and that may matter more if anyone in the house has asthma, bronchitis or other breathing issues, which is worth its own page. The best insulation if you have asthma. CSR Bradford SUIS, FBS-1 Glasswool — §3 Composition (printed p.2 of 8) plus §11 Toxicological Information, Health Effects (Acute, Inhaled), printed p.6 of 8 ↗
So the sentence I will put my name to is this: glasswool does not cause silicosis and it is still a respirable-fibre irritant that its own paperwork tells you to keep out of your eyes, off your skin and out of your lungs.
The classification history, in full
Fibreglass insulation used to carry the higher cancer rating. IARC moved it down in 2001. Here is exactly what both ratings mean.
I have put this near the bottom on purpose because it is not my argument and I am not leading with somebody else's cancer classification. It is worth knowing properly though, in both directions.
Group 2B
“Possibly carcinogenic to humans”
IARC’s working group met in Lyon in October 1987 and published as Monograph 43 in 1988. Their words: “Glasswool is possibly carcinogenic to humans (Group 2B).” The basis was sufficient evidence of carcinogenicity in experimental animals — mostly injection studies of that era — and inadequate evidence in humans.
Group 3
“Not classifiable as to its carcinogenicity to humans”
A new working group met in Lyon over 9 to 16 October 2001 and published as Monograph 81 in 2002. Their words: “Insulation glass wool, continuous glass filament, rock (stone) wool and slag wool are not classifiable as to their carcinogenicity to humans (Group 3).” The animal evidence was downgraded from sufficient to limited.
IARC Monographs Vol. 81, Man-made Vitreous Fibres (2002), Summary & Evaluation ↗
Why it changed, which is the interesting part
Two things happened across the fourteen years between the evaluations. The first is that manufacturers changed the glass. IARC’s own general remarks note that some manufacturers altered the chemical compositions of their products to enhance their solubility in biological systems, that others developed completely new products, and that the more significant changes took place in the early 1990s. IARC Monographs Vol. 81, General Remarks ↗ A new generation of chronic inhalation and biopersistence studies across eleven fibre types then showed carcinogenic potential tracks how long a fibre survives in a lung rather than simply whether it is a fibre. The biosoluble insulation wools caused no fibrosis and no tumours in rodents even after lifetime exposure at high levels.
The second is that the worker studies got a lot better. The US cohort grew to 16 plants and extended follow-up to 1992; the European cohort extended follow-up to 1990 across 13 plants. With those longer runs of data, the human evidence still came back inadequate rather than positive. IARC Monographs Vol. 81, General Remarks — US cohort to 1992, European cohort to 1990 ↗ The US National Toxicology Program independently reports the same finding for its own cohort. NTP Report on Carcinogens, 15th ed., Certain Glass Wool Fibers (Inhalable), pp.2–4 ↗
Four things not to over-read out of that downgrade
One.Group 3 is not IARC saying something is safe. Their current preamble spells it out: “An evaluation in Group 3 is not a determination of non-carcinogenicity or overall safety. It often means that the agent is of unknown carcinogenic potential and that there are significant gaps in research.” Preamble to the IARC Monographs (2019), p.36 ↗
Two.The downgrade covers insulation-grade wool. The durable special-purpose glass microfibres and refractory ceramic fibre were not downgraded and remain Group 2B, so “all fibreglass was cleared” is not a true sentence.
Three.Pre-2001 batts still sitting in plenty of Australian roofs today were made to the higher-rated Group 2B product spec, per the industry’s own account of when the reformulation happened. They look identical to current stock from the manhole.
Four.This one is my own reading of two dated facts rather than a single source stating it outright: the worker-cohort follow-up behind the 2001 downgrade ran only to 1990–1992, a year or two after the reformulation the industry itself dates to the early 1990s. I have not found a published human cohort study with anything like a 25-year follow-up on workers exposed mainly to the reformulated fibres. That’s a narrow claim, and I would welcome a source that closes it if one exists.
Where I land and the choice in front of you
So — are fibreglass batts safe to leave above your bedrooms? Here is where I land after nearly forty years in Brisbane roofs.
A decision this size needs the real numbers beside it, so here is the choice laid out from the same documents already linked on this page.
On one side, a fibreglass batt sheds fine glass fibre — 10 to 20% of it under the 3-micron size that reaches deep into a lung — and once that fibre is airborne it does not settle politely back onto the ceiling. It goes wherever the air in your roof is going, sitting in the space above every room in the house for as long as that air stays disturbed. I have worked out roughly how many kilograms of that fibre sit above an average Brisbane roof on the dust breakdown page. It is not a small number. How much fibreglass dust ends up in your house.
On the other side, Cellulose Fibre Insulation is a coarse plant fibre treated with boric acid. It drops where it is put rather than floating off through the house.
Fibreglass batts or Cellulose Fibre Insulation — the comparison I'd want before deciding what goes above my own family's bedrooms
You can afford the better, natural product and you are still not sure which way to go. This is the comparison I would want in front of me.
On one side, microscopic glass particles small enough to drift through the house unseen and be breathed deep into your lungs. The industry’s own national code puts 10 to 20 per cent of glasswool fibre under the 3-micron respirable size, written for the coarser 5 to 8 micron glasswool of 1990. NOHSC:2006(1990), Schedule 3 (Glasswool) §7, printed p.42 (PDF p.50) — “nominal fibre diameter of between 5-8 µm … in the order of 10 to 20 per cent” ↗ Knauf’s current Australian sheet has the fibre finer again at 3 to 5 microns. Knauf Insulation AU/NZ SDS KI_DP_101, rev 3.0, 30/07/2020, section 9, p.7 — “Nominal diameter of fibres 3 - 5 μm” ↗ A finer fibre puts more of itself under that 3-micron line rather than less.
Your family gets none of the gear the manufacturer’s own sheet puts on its installers. That sheet asks for long sleeves, long trousers and gloves to AS 2161, dust goggles to AS/NZS 1336 for overhead work in enclosed or poorly ventilated areas such as ceiling spaces and a P1, P2 or N95 respirator wherever dust is generated in a space like that. CSR Bradford SUIS, FBS-1 Glasswool, §8 Exposure Controls / Personal Protection, printed p.4 of 8 — “ventilated non-fogging dust resistant goggles … such as ceiling spaces or risers … P1, P2 or N95 type respirators are appropriate” ↗ Your family lives under that ceiling for decades while an installer works above it for a morning. The ways down are already cut into the plasterboard: every exhaust fan, every flue, every downlight and every time somebody opens the manhole.
That is glass your body has no use for, against a plant fibre treated with boric acid — boron, which you can buy over the counter at any chemist as a bone and joint supplement. The manufacturers describe their modern batt as bio-soluble and market it as low-irritant. CSR Bradford SUIS, FBS-1 Glasswool, §3 Composition, printed p.2 of 8 — “Mineral Glasswool fibre (amorphous, non-crystalline, bio-soluble – Note Q applicable)” ↗ Both of those words are about how fast a fibre dissolves once it is inside you and about how little it prickles your arms. Neither one keeps a 3-micron particle out of the air above your bedrooms.
I don’t like the idea of breathing in invisible particles drifting down out of the roof and never knowing about it. Every customer makes that call for themselves. My job is to hand you the manufacturers’ own facts, not a sales pitch.
Do you have fibreglass batts in your roof now? We can quote to take them out or to pump Cellulose Fibre Insulation straight over the top of them.
Neither of the two products we recommend sheds a particle small enough to be breathed deep into your lungs. Cellulose Fibre Insulation was measured at under 0.1% respirable dust by the NIH. That trace fraction held no plant fibre in it at all. NTP TOX-74 (NIH), August 2006, plain-language summary p.5 — “less than 0.1% were of the size that were respirable by the lung” ↗ The polyester manufacturer’s own sheet says any free fibres are not of respirable size. Autex GreenStuf / QuietStuf polyester MSDS, Australia — “any free fibres which may be present are not of respirable size” ↗ Both of them have fibres. Neither of them has the inhalable fraction that puts 10 to 20 per cent of glasswool fibre under 3 microns. Cellulose Fibre Insulation · Polyester batts
Check every bit of it yourself
Every fibreglass and insulation safety document behind this page is one you can open yourself.
Government, university and peer-reviewed links are followed. Manufacturer, retailer and patent links carry nofollow. The raw URL is printed under each one so you can still find the document if a site moves the page.
The definition of a respirable fibre
“Respirable fibre is a particle with a diameter less than 3 micrometres and a length greater than 5 micrometres and with a length to width ratio of greater than 3:1.”
https://www.safeworkaustralia.gov.au/system/files/documents/1702/nationalstandard_syntheticmineralfibres_nohsc1004-1990_pdf.pdf
How much of a glasswool batt is under 3 microns
“Glasswool is generally manufactured to a nominal fibre diameter of between 5-8 µm … The typical proportion of fibres less than 3 µm contained in glasswool materials is in the order of 10 to 20 per cent.”
https://www.safeworkaustralia.gov.au/system/files/documents/1702/nationalstandard_syntheticmineralfibres_nohsc1004-1990_pdf.pdf
The same figure for rockwool — the biggest measured share in this table
“The typical proportion of fibres less than 3 µm contained in rockwool materials is in the order of 15-25 per cent.”
https://www.safeworkaustralia.gov.au/system/files/documents/1702/nationalstandard_syntheticmineralfibres_nohsc1004-1990_pdf.pdf
Current Australian glasswool batt safety data sheet — fibre size
“Appearance: Solid. Rolls. Panel. Loose fibre. … Nominal diameter of fibres 3 - 5 μm”
https://pim.knaufinsulation.com/files/download/knauf-insulation-aunz-msds_v0.1.pdf
Blow-in glasswool safety data sheet — the finer fibre
“Nominal diameter of fibres 2 - 5 μm. Length weight geometric mean diameter less 2 standard errors < 6 μm. Orientation of fibres: Random.”
https://pim.knaufinsulation.com/files/download/ki_dp_109__glass_blowing_mineral_wool_uk_en.pdf
Knauf's own Jet Stream MAX product datasheet — unbonded
“Jet Stream® MAX is an unbonded, glasswool insulation designed with optimal thermal properties and excellent coverage and blowing characteristics… Equipment required: To achieve the required R-value, this product must be installed using an approved blowing machine and equipment.”
https://pim.knaufinsulation.com/files/download/kian0815220ds_jet_stream_max_ceiling_datasheet_v0.1_603f2124c65f3.pdf
Measured airborne fibre — batts vs loose fill, 107 houses
“Respirable-fiber concentrations during installation of glass wool batt insulation in homes ranged from 0.02 to 0.41 fibers/cm³, with a mean of 0.14 … The installation of loose fiberglass insulation with a binder resulted in mean exposures of 0.55 fibers/cm³ for the installer … The highest exposures were noted for installation of loose insulation without binder; exposure levels ranged from 1.32 to 18.4 fibers/cm³ (mean = 7.67 fibers/cm³) for installers.”
The manufacturer's own fibre-diameter and itch figures
“…glass fibers 130 having a smaller diameter than the glass fibers used in conventional residential fiberglass insulation products, which have fiber diameters typically greater than 4 μm (15.7 HT). In particular, the exemplary fibrous insulation product 100 may include glass fibers 130 having an average fiber diameter… in the range of 2.03 μm (8.0 HT) to 3.04 μm (12.0 HT)…”
https://patents.google.com/patent/US12297342B2/en
Fibreglass is amorphous, not crystalline, silica
“These fibers differ from natural mineral fibers such as asbestos because they do not have a crystalline molecular structure. The randomly oriented molecular structure of synthetic vitreous fibers is called an amorphous structure.”
https://www.atsdr.cdc.gov/toxprofiles/tp161.pdf
Crystalline silica is Group 1, amorphous silica is Group 3
“Crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1). … Amorphous silica is not classifiable as to its carcinogenicity to humans (Group 3).”
https://www.inchem.org/documents/iarc/vol68/silica.html
Crystalline vs amorphous silica, tested side by side
“HPRT assays conducted in alveolar epithelial cells of rats exposed to crystalline and amorphous silica (3 and 50 mg/m³ respectively) via inhalation exposure for 13 weeks showed that mutation frequency was significantly increased in rats exposed to crystalline silica but not amorphous silica.”
https://www.industrialchemicals.gov.au/sites/default/files/Crystalline%20silica_Human%20health%20tier%20II%20assessment.pdf
Silicosis is caused by the crystalline form specifically
“Silicosis is caused by inhaling dust that contains free crystalline silica. The development of silicosis is influenced by several factors, which include: … Form of the silica (e.g., crystalline, or amorphous)…”
https://www.ccohs.ca/oshanswers/diseases/silicosis.html
The manufacturer's own sheet on glasswool installation dust
“Unprotected exposure to high levels of dust of these products (during installation or removal) may cause discomfort of the nose, throat, and upper and lower respiratory tract, especially in persons suffering from upper respiratory or chest complaints such as hay fever, asthma or bronchitis.”
https://pricewiseinsulation.com.au/wp-content/uploads/2019/04/Bradford-Glasswool-Insulation-Safety-Data-Sheet.pdf
The gear the glasswool manufacturer puts on its own installers
“Direct skin contact can be minimised by wearing long-sleeved shirts and long trousers, a cap or hat, and standard duty gloves conforming to Australian Standard AS 2161. … particularly overhead or in enclosed or poorly-ventilated areas such as ceiling spaces or risers, eye contact with dust or fibre can be avoided by wearing ventilated non-fogging dust resistant goggles… If dust is generated in enclosed or poorly-ventilated areas, an approved particulate respirator… P1, P2 or N95 type respirators are appropriate.”
https://pricewiseinsulation.com.au/wp-content/uploads/2019/04/Bradford-Glasswool-Insulation-Safety-Data-Sheet.pdf
IARC moved insulation glass wool from Group 2B to Group 3
“Insulation glass wool, continuous glass filament, rock (stone) wool and slag wool are not classifiable as to their carcinogenicity to humans (Group 3).”
https://www.inchem.org/documents/iarc/vol81/81.html
Measured respirable fraction of cellulose insulation dust
“Of the cellulose insulation particles examined by the generator, less than 0.1% were of the size that were respirable by the lung.”
https://ntp.niehs.nih.gov/sites/default/files/ntp/htdocs/st_rpts/tox074_rev.pdf
Polyester fibre size and handling
“The fibres used in the thermal bonded insulations comprise of 100% polyesters and may range from 8 micron to 40 micron in diameter … any free fibres which may be present are not of respirable size … No protective clothing or gloves are required when handling or installing Autex insulation.”
https://thermacon.com.au/wp-content/uploads/2014/01/Autex-Material-Safety-Data-Sheet.pdf
One note for the record. The CSR Bradford Safe Use Information Sheet above is a reseller-hosted mirror of the genuine document, identifiable by its own CSR-SHE-Glasswool SUIS reference and its 23 June 2015 issue date — CSR’s own direct link now redirects to their homepage after a brand consolidation. And the Knauf blow-in fibre figure comes from the UK and US sheets for product number KI_DP_109, since I could not find an Australian-region SDS that names Jet Stream MAX by trade name — the Australian sheet for the same manufacturer’s glasswool covers rolls, panel and loose fibre under one document at 3 to 5 microns, which is the same fibre class.
Common questions
Are fibreglass batts safe? Questions I get asked on site, answered.
Are fibreglass batts safe to have in my roof?+
Once it is laid and left alone most of the fibre stays where it was put. The trouble starts the moment somebody disturbs it, which in a real house is every electrician and every plumber and every antenna bloke for the next thirty years. Cutting a batt or dragging one aside or pulling one out puts fibre into the air. The 1990 national code for synthetic mineral fibres puts 10 to 20% of glasswool fibre under 3 microns across, which is the width that code itself says reaches the deepest part of the lung. This is not a cancer claim — IARC moved insulation glasswool down to Group 3, not classifiable, back in 2001. I take them at their word on that. My argument is about the size of the particle and what that means for how much of it ends up in a lung rather than caught by a nose and throat on the way through.
What is a respirable fibre? And why is it thinner than 3 microns AND longer than 5 microns?+
That is not a typo and it catches everybody out the first time. A fibre is a needle, so it has two measurements. The definition uses both of them. Thinner than 3 microns across is what lets it ride the air past your nose and your throat instead of being caught on the way through. Longer than 5 microns is what stops the cleaning cells in your lung from wrapping it up and shifting it back out again. That's thin enough to get all the way in and long enough to be hard to get back out. The 1990 national code words it as a particle with a diameter less than 3 micrometres and a length greater than 5 micrometres and a length to width ratio greater than 3 to 1. That same definition is used by the World Health Organization and by NIOSH.
Is fibreglass the same silica that causes silicosis?+
It is the same base chemistry and a different physical form. The form decides everything. Fibreglass is essentially glass. Glass is a silicate melted out of sand, so at the element level fibreglass is silica. But glasswool is amorphous silica, meaning the molecules sit in no particular order. Silicosis is caused by respirable crystalline silica — the dust off cutting and grinding stone, concrete and engineered stone, where the molecules sit in a rigid repeating pattern. Safe Work Australia says plainly that crystalline is generally the more hazardous form. The glasswool manufacturer's own composition sheet lists the fibre itself as amorphous, non-crystalline, at over 85% of the product — the remaining share on that sheet is an organic binder, not a crystalline fraction of the glass. So fibreglass does not cause silicosis. That is different from fibreglass being harmless: the manufacturer's own sheet still documents nose, throat and upper respiratory discomfort from installation dust. That may matter more for anyone with asthma, bronchitis or other breathing issues.
Can you see fibreglass dust in the air?+
It isn't the part that matters — that's the bit that catches people. The code itself gives the scale, saying a strand of human hair is approximately 50 micrometres in diameter, so a 3-micron glass fibre is about a seventeenth the width of a hair off your own head — small enough that no naked eye will ever pick out a single one. What you can see in a shaft of sunlight through the manhole is the coarse stuff. The fine fraction is up there with it, doing nothing at all to announce itself.
Is loose-pumped fibreglass (like Knauf Jetmax) worse than fibreglass batts for dust?+
On the fibreglass-vs-fibreglass numbers that exist, yes — laying glasswool batts averaged 0.14 respirable fibres per cubic centimetre for the installer in a field survey of 107 houses. Pumping loose fibreglass that DID have a binder averaged 0.55 for the installer, roughly four times higher. Loose fibreglass with no binder at all ran highest of the lot, averaging 7.67. That 1993 study measured the general category rather than any specific current product, so the 7.67 figure should not be hung on any one brand. What I can tell you about a product like Jetmax specifically is what its own manufacturer's datasheet says: it is unbonded, meaning it has no binder holding the fibre together at all, which puts it closer to the highest-exposure category than the lowest one — though nobody has published a respirable-fibre figure for that exact product, so I have not put a number against it on this page.
Why did fibreglass stop itching so much? And is that a good thing?+
They made the fibre finer. Finer cuts both ways. Owens Corning's own patent says conventional residential fibreglass has fibre diameters typically greater than 4 microns and that its new low-itch product runs 2.03 to 3.04 microns, measured against the wool industry's own prickle standard on a Wool Comfort Meter. The old specimens scored between 150 and 267. The new fine-fibre ones still scored between 57 and 140 — roughly half the old prickle number, not zero. The catch is in the government's own carcinogen profile: thinner fibres are deposited deeper into the lung. It cites work finding that operations making smaller-diameter fibre put airborne fibre concentrations many orders of magnitude higher into the air, with more of those fibres of respirable size. A more comfortable batt is a finer batt. That means more of it can be inhaled deep into your lungs when you use batts like this in your home.
Was fibreglass ever classified as a possible carcinogen?+
Yes, it carried the higher rating for thirteen years. IARC, the World Health Organization's cancer agency, classified glasswool in 1988 as Group 2B, possibly carcinogenic to humans, on sufficient evidence in animals and inadequate evidence in humans. In October 2001, published as Monograph 81 in 2002, IARC re-evaluated and moved insulation glass wool down to Group 3, not classifiable as to its carcinogenicity to humans, since the animal evidence was downgraded from sufficient to limited. What changed between the two evaluations was the product: manufacturers reformulated the glass to dissolve faster in lung fluid. The new biosoluble fibres caused no fibrosis and no tumours in rodents even after lifetime high-dose exposure. Worth reading properly though — IARC's own preamble says a Group 3 evaluation is not a determination of non-carcinogenicity or overall safety. Any batt made before the reformulation is a Group 2B product by its own era's paperwork, sitting in plenty of roofs today looking identical to the current stock.
People say Cellulose Fibre Insulation is the loose dusty one — is that right?+
It is backwards. It is the single most common thing I correct on the phone. People picture Cellulose Fibre Insulation as a loose heap of paper blowing everywhere and picture a batt as tidy because it comes in a pack. The measured numbers go the other way. The NIH generated cellulose insulation dust the way an install generates it and found under 0.1% of the particles were of respirable size and that the respirable fraction held no cellulose material in it. The same field survey that measured batt installation found loose fibreglass with a binder averaging 0.55 respirable fibres per cubic centimetre for the installer against 0.14 for laying batts. Ours is a heavier, coarser plant fibre that drops where it is put; theirs is a 2 to 8 micron glass filament that goes where the air goes. I have the full kilogram-by-kilogram breakdown of what that means for a real roof on a separate page.
Should I get the old fibreglass out of my Brisbane roof?+
It depends what is up there. I will price both ways rather than push one. If the batts are sunken, gappy or full of rodent nests then removal and a pump of Cellulose Fibre Insulation is the job I would do — after more than 6,000 houses I can tell you the removal is the part nobody enjoys because the product is itchy and normally stinks of rat urine. If the batts are still in reasonable shape then a top-over with cellulose fibre keeps whatever value they have, fills every gap, covers the joists, and puts a seamless blanket over the old fibre so it stops getting stirred up every time somebody goes up there. Send me your address and I will price both.
Real reviews, real jobs
What our customers say
Genuine Google & hipages reviews from Comfort Zone customers across SE Queensland.
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Angela M.
SE Queensland
“The fact that I can't even tell it's 6 degrees outside when I wake up in the morning speaks for itself. Have wasted so much money attempting to heat and cool an uninsulated home. Worth every $.”
- Phipages
P Peter
Alstonvale, 2024
“Connected with Comfort Zone Insulation and would recommend them”
- J
Jessa B.
Brisbane
“It dropped about 4 degrees straight away, and we added another 3 with the second job. I appreciate Peter's honesty, and the team showed pictures before and after.”
- Nhipages
Nola M
Birtinya, 2024
“They were courteous and competent.”
- I
Iain V-B.
Brisbane
“Quick and polite service. Great follow-up advice and photos sent for our records. Above and beyond what we expected. Would highly recommend.”
- Jhipages
Jennifer's E
Upper Caboolture, 2024
“Excellent customer service. Highly recommended. Has a profound knowledge of insulation products and has the best interest of his customer.”
- G
Gerry S
Fitzgibbon, 2023
“I used Comfort Zone and they have a done an excellent job.”
- Jhipages
Jennifer
Upper Caboolture, 2024
“Excellent customer service. Highly recommend. Has a profound knowledge of insulation products and has the customer best interest.”
- J
Jung K
Riverhills, 2023
“An experienced family operation. Highly recommend. Thank you for the great job!”
- Dhipages
Diane A
Ormeau, 2024
“Peter and crew did a great job I would definitely recommend them”
- D
David H
Sunshine Coast, 2021
“Completed the job as quoted and to a high standard. Great personal service. Would highly recommend Comfort Zone for ceiling installation work.”
- Thipages
Timea
Highland Park, 2023
“I was extremely satisfied with the service they provided. They gave a very thourough explanation of the materials used, the way the work will be carried out and the price I had to pay was the exact amount quoted, no hidden costs included. They arrived on time, well prepared and workwas carried out exactly how they said it would be, they were super efficient, well prepared and were kind enough to even clean up after themselves. The services they provided was second to none! I don't hesitate to recommend them for any insulation job!”
- B
Benjamin H
Carseldine, 2019
“Very good explanation about their works. Advice of existing problems with the roof. Clean work. Very professional.”
- Mhipages
Mark
Pottsville, 2017
“Michelle, we are done - Peter from comfort zone insulation was very helpful. very honest with his recommendations - in fact he told me that the product my daughter had if installed correctly was superb. Thanks Peter you are a champion and i would recommend you to any person that was wanting professional advice and old school service.”
- I
Ian G
Burnside, 2019
“Good information, communication and professionalism.”
- Jhipages
Jessica
Pottsville, 2016
“This business offers a fantastic product that other businesses did not. Pump in ceiling insulation. Knowledge of the industry second to none.”
- D
Danny D
Boondall, 2018
“He explained everything he was going to do and the different types of insulation they used. He talked through the different options but made a recommendation for the one most people use, which is the one I chose. He was very understanding towards what I needed and not about himself.”
- Jhipages
Jack
Pottsville, 2023
“Excellent communication and informative. Professional.”
- G
Graham R
Riverhills, 2018
“Comfort Zone. Turned up ahead of time, completed in about 2 hours, cleaned up. All good. Very motivated installation team.”
- Thipages
Tony P
Redland Bay, 2023
“Very knowledgeable about insulation”
- A
Alex B
West Ipswich, 2018
“Fast, friendly, efficient.”
- Shipages
Steve
Redland Bay, 2017
“Excellent job and reasonable price.”
- L
Luke D
Mcdowall, 2017
“Peter did a good job. It was a quick and clean service. I'm happy to recommend!”
- Bhipages
Bruce H
Kuluin, 2023
“Prompt and efficient quoting.”
- B
Brendon
Brays Creek, 2016
“Peter supplied and installed roof insulation for me. He was very informative and provided good advice.”
- Ghipages
Gerry S
Fitzgibbon, 2023
“I used Comfort Zone and they have a done an excellent job.”
- T
Trevor G
Brookside Centre, 2016
“Excellent tradesmen from Comfort Zone Insulation. They were punctual and cleaned up after. Highly recommended.”
- Thipages
Tamara
Underwood, 2023
“Peter is honest, hard-working and came on time. Knew excally what he was talking about and answered my questions. Would 100% recommend”
- J
John G
Beaudesert, 2019
“Peter is an honest person who provided me with the information I wanted then performed a good job with great results for the benefit of myself and my family.”
- Shipages
Sterling G
Ashgrove, 2023
“Comfort Zone were very knowledge with great communication and follow up”
- Ghipages
Graham R
Riverhills, 2018
“Comfort Zone. Turned up ahead of time completed in +- 2 hours cleaned. All good. Very motivated installation team”
- Jhipages
Jung K
Riverhills, 2023
“An experienced family operation. Highly recommend. Thank you for the great job!”
- Khipages
Kathy A
North Lakes, 2023
“We connected with Peter through HiPages and he was prompt, professional and even came back after the job was complete to assist with a question we had. We would highly recommend Peter for further insulation works.”
- Dhipages
David H
Sunshine Coast, 2021
“Completed the job as quoted and to a high standard. Great personal service. Would highly recommend Comfort Zone for ceiling installationn work.”
- Shipages
Sue H
Sunshine Coast, 2021
“Incredible customer service”
- Ehipages
Eileen C
Cedar Vale, 2021
“Quality work, good customer service, prompt”
- Chipages
Craig M
Woody Point, 2021
“Called within 5 minutes of request. Very knowledgeable and explained job in great detail, provide great advice in prior preparation for works required. Very friendly and helpful.”
- Jhipages
Jenny C
Plainland, 2021
“Although I did not hire Peter I was impressed with the initial contact and the knowledge he was willing to impart. I was treated with respect which I appreciated. I would have hired but I received a lower quote.”
- Qhipages
Quinton
Coomera, 2020
“Professional installation without any short cuts. True to their word with high integrity. Response from Comfort Zone Insulation”
- Ghipages
Gary P
West Kempsey, 2020
“Came & Gave a free quote”
Get a fixed quote to replace or seal in the fibreglass in your Brisbane roof.
Send me your address and I’ll price both jobs for you. One is pulling the old glasswool out and pumping Cellulose Fibre Insulation. The other is capping the downlights and topping straight over it so the fibre stops getting stirred up every time somebody goes up there. Fixed price, usually within 48 hours, no deposit and no pre-quote inspection. If what you have up there is still doing its job I’ll tell you that too. We insulate homes right across Brisbane and SE Queensland.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986