FAQ · Fire safety
Is cellulose insulation fire-resistant?
Yes. It’s been shown to slow fire spread. Cellulose is treated with borax, which melts at about 734°C, roughly 200° above a house fire. Hold a blowtorch to it and it chars and glows where the flame touches, then stops, while fibreglass batts simply melt away.
It’s the first thing people ask when I tell them their insulation is going to be recycled paper: “won’t that just catch fire?” It’s a fair question, and the answer is that the treatment changes everything. Here’s the chemistry, the demonstration you can watch, and how cellulose stacks up against a melting batt. With the government sources to back it.
It’s paper, but it’s treated paper.
Cellulose is made from recycled waste paper, so the worry is reasonable: paper burns. The thing that changes it is the treatment. The Australian Government’s CSIRO describes cellulose fibre as pulverised paper combined with fire-retardant chemicals, and the chemical we use is borax. Borax is a natural mineral salt that melts at about 734°C, and that figure matters, because it’s roughly 200° above the temperature of a typical house fire. So the fire-retardant stays doing its job right through the heat range a house fire reaches. (That’s the borax chemistry, not a fire rating on the product. There’s a difference, and I’ll come to it.)
The state-government guidance is even more direct about what the treatment does. Sustainability Victoria’s Energy Smart Housing Manual states that cellulose fibre must be treated with a fire retardant such as borax, and that the treatment ensures that, if the material does ignite, the flame will not spread. That’s a government source saying the quiet part out loud. It’s not the paper that matters, it’s what we put in the paper.
The demonstration you can watch
Hold a blowtorch to it. It chars and glows, but won’t carry a flame.
You don’t have to take my word for the chemistry. Take a handful of our treated cellulose and put a blowtorch straight on it. Where the flame touches, it chars and glows orange, but the moment you take the torch away, it stops. It won’t carry the flame across the rest of the blanket the way a sheet of newspaper would, because the borax has done exactly what Sustainability Victoria describes: stopped the flame spreading.
And here’s the bit people don’t expect. As it chars, it gives off only carbon dioxide and steam, not the gases a fibreglass batt’s binders produce when they burn. The relevant Australian fire test for building materials is AS 1530.1, which measures ignitability, flame spread, heat and smoke , borate-treated cellulose is made to be tested against it. I’ll show you the manufacturer’s certificate for the real numbers rather than quote a rating from memory.
The contrast
Fibreglass melts away. Cellulose chars and holds.
Fibreglass is glass, and glass melts. In a house fire the batts soften and melt away, leaving your roof timbers exposed at the worst possible moment, and the binders holding the batts together give off gases as they burn. So the cheapest insulation in the roof also disappears right when you most need cover. Borate-treated cellulose does the opposite: it chars and holds its position rather than melting, and it gives off only carbon dioxide and steam.
Here’s the plain version, because it’s more convincing than the hype anyway: nothing in your ceiling makes a house fireproof, and I’m not claiming it does. What I’m telling you is that when you put the two materials in the same heat, the cellulose stays put and resists carrying a flame, while the batt melts out of the way. That difference, backed by the CSIRO and Sustainability Victoria, not just by me, is one more reason cellulose is the only product I’d use in my own home.
“People hear ‘recycled paper’ and picture a bonfire. Then I put a blowtorch on a handful in front of them and it just chars and stops. That’s the borax doing its job.”Peter Johnson, Comfort Zone Insulation Team
“The big burn”
The demonstration people Google, and the footnote you need on it.
If you search for this, you’ll find a famous demonstration called “the big burn,” where mock structures were lit to compare insulations. The write-up reports the fibreglass-insulated building’s ceiling collapsed about 21 minutes in, while the cellulose-insulated structure’s ceiling held for over an hour and its walls were still standing at the three-hour mark. It lines up exactly with what I see in my own blowtorch test.
But here’s the footnote, because I’d rather you trusted me than caught me out: that test was done in the United States in 1978, so it’s a demonstration, not an Australian fire rating. I’ll never dress up a foreign, decades-old demo as if it were a certified Australian result. For the actual Australian numbers, the AS 1530.1 ignitability and flame-spread figures, ask me for the manufacturer’s test certificate and I’ll show you the real results rather than print a rating I can’t back up on the page.
Watch the fire tests for yourself
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Some of these were filmed a while back. Our methods, safety standards and products have moved on since. For how we work today, see the rest of this page.
More on cellulose and fire
Is cellulose insulation fire-resistant?+
Yes. It's been shown to slow fire spread. Cellulose is treated with borax during manufacture, and Sustainability Victoria's government guide states that the borax fire-retardant treatment ensures that if the material does ignite, the flame will not spread. Borax melts at around 734°C, roughly 200° above the temperature of a typical house fire, so hold a blowtorch to a handful of treated cellulose and it chars and glows where the flame touches, then stops, rather than carrying the flame across the rest. That's a demonstration you can watch, not a marketing line. It also gives off only carbon dioxide and steam as it chars, rather than the gases that fibreglass batt binders produce. I won't print a fire rating without showing you the test certificate, but the borax chemistry and the government's own wording are why I trust it in a roof. Including my own.
Won't paper insulation just catch fire?+
It's the obvious worry, and it's a fair one. Cellulose is recycled paper, and paper burns. The difference is the treatment. The CSIRO describes cellulose fibre as pulverised paper combined with fire-retardant chemicals, and the chemical we use is borax. Borate-treated cellulose has been shown to slow fire spread: Sustainability Victoria's Energy Smart Housing Manual says the borax treatment ensures that if the material does ignite, the flame won't spread. Untreated newspaper in a pile is a fire risk. Borate-treated cellulose, pumped into your ceiling, behaves completely differently: under a blowtorch it chars and glows where the flame touches it, then stops, rather than carrying the flame across the rest of the blanket. The fire test for building materials in Australia is AS 1530.1, which measures ignitability, flame spread, heat and smoke, and borate-treated cellulose is made to be tested against it.
What happens to fibreglass batts in a house fire?+
Fibreglass is glass, and glass melts. In a house fire the batts soften and melt away, leaving your roof timbers exposed where you most needed the cover, and the binders that hold the batts together give off gases as they burn. So the cheapest insulation also disappears at the worst possible moment. Cellulose does the opposite: it chars and holds rather than melting, and gives off only carbon dioxide and steam. I'm not telling you cellulose makes a house fireproof; nothing in your ceiling does that. What I'm saying is that when you compare the two materials in the same heat, borate-treated cellulose has been shown to slow fire spread, it stays put and resists carrying a flame, while a batt melts out of the way. That's one more reason it's the only product I'd use in my own home.
Have they actually burned cellulose against batts to test it?+
There's a well-known demonstration people Google called "the big burn", but be clear that it was a United States test from 1978, not an Australian fire rating, so I'll always present it as a demonstration rather than a certified result. In it, three mock structures were lit, and the write-up reports the fibreglass-insulated building's ceiling collapsed about 21 minutes in, while the cellulose-insulated structure's ceiling held for over an hour and the walls were still standing at the three-hour mark. It lines up with what I see in my own blowtorch test and with what the Australian government sources say about borax stopping flame spread. For the actual Australian numbers, the AS 1530.1 ignitability and flame-spread figures, ask me for the manufacturer's test certificate and I'll show you the real results rather than quote you a rating off the top of my head.
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Or call Peter on 0414 586 315 , happy to do the blowtorch demonstration on your kitchen bench so you can see it for yourself.