The best insulation if you have asthma, built on the glasswool industry’s own safety sheet.

I can't hand you a medical answer, because I'm an insulation contractor and not a doctor. What I can hand you is the airborne-particle comparison, since that's the part I actually measure and source. Polyester batts carry a maker's safety data sheet stating any free fibres present are not of respirable size at all. Cellulose Fibre Insulation sheds under 0.1% respirable dust by the NIH's own measurement, and it's a coarse fibre that drops where it's pumped rather than a fine filament that rides the air. Fibreglass batts run 10 to 20% respirable fibre by the industry's own 1990 code, and the makers' own safety sheet names hay fever, asthma and bronchitis as reasons that dust discomfort matters more for some people. If a breathing condition is in the house, that's the order the documents put those three products in.

The glasswool makers' own paperwork says so directly. CSR Bradford's Safe Use Information Sheet for FBS-1 Glasswool states that 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. That's their document, not mine, and it's the whole reason this page exists.

On the airborne-fibre measure, yes, and the makers' own documents are what say so. Autex's material safety data sheet for its GreenStuf polyester batts states any free fibres present are not of respirable size — nothing to breathe deep into a lung. There's no dust mask on the instructions, no eye or skin warning on the sheet, and I rub a batt on my own face in front of customers to show there's nothing in it to itch. It's the same fibre as a pillow or a doona.

I'm not going to call it "asthma-safe" or "hypoallergenic," because neither of those is a claim any document backs and I won't put a label on a product that the paperwork doesn't support. What I can tell you is the measured number. The NIH generated cellulose dust the way an install generates it and found under 0.1% of the particles were of respirable size at all, and that the respirable fraction held no cellulose material in it — mostly the fire retardant and clay. It's still dusty work going in, the same NIH report found total dust over the American limit on some cellulose sites and about 33% of workers reporting sore eyes, which is why my crew wears the same respirator on our own product that we wear on anybody else's. Once it's pumped and the roof's sealed back up, it sits there — nobody's up there disturbing it every time a light needs changing, unlike a batt.

I've never seen a sign, and I look every time I'm in one. The safety data sheet for what's on the shelf is a free public PDF, and it says plainly to minimise eye and skin contact and inhalation during handling — but that sheet doesn't come with the trolley. You have to already know to go and find it. I'm not accusing any particular retailer of doing something unlawful. I'm saying the document exists, the aisle doesn't mention it, and a split pack sitting at chest height in a walkway is real exposure to real people who never read that PDF.

It depends what's up there and I'll price both ways rather than push one. Old, sunken or gappy batts are worth pulling and replacing — a full removal and a pump of Cellulose Fibre Insulation stops the fibre being disturbed every time a tradie's up there. If the batts are still in reasonable shape, a top-over with cellulose seals a blanket over them so they stop getting stirred up, without the cost of a full rip-out. Either way, get the fibreglass out of arm's reach of anyone climbing into that roof.

No, and that's an important distinction even on a page about breathing conditions. Glasswool is amorphous silica — the molecules sit in no particular order — while the silica that causes silicosis is crystalline, the dust off cutting and grinding stone, concrete and engineered stone. Safe Work Australia says plainly that crystalline silica is the more hazardous form. Fibreglass not causing silicosis isn't the same as fibreglass being harmless to breathe, which is the whole point of this page — but it's a different hazard to a different disease, and I'm not going to blur the two.

Every downlight, exhaust fan, range hood duct and manhole is a hole between the roof and the room under it, and the roof space is never still air. Fine glass fibre that's disturbed goes where the air goes rather than dropping straight back down. We've written up the full physics — settling times, how far particles travel, what a real Queensland roof does to them — on our fibreglass dust page.