Why cellulose fibre · The technical case
Why I only recommend pumped-in cellulose fibre.
Pumped-in cellulose fills every gap, so it delivers about 40% higher effective R-value than batts after install. It’s borax-treated so pests won’t live in it and to slow fire spread, handles a roof leak, and carries a transferable life-of-house guarantee.
I’m Peter Johnson. After 40 years and 6,000 roofs, about 92% of my customers end up choosing cellulose. Here are the fourteen reasons it’s the only product I’d put in my own mother’s house, every figure cited to a real source you can check.
One seamless blanket
no gaps, full contact, every corner
Came here for a batt quote? Read this first
The only product I’d put in my mother’s house.
In the end about 92% of my customers go with the pump-in cellulose fibre insulation, 6% with polyester batts (the King of batts, locally made and non-itchy) and just 2% with the cheap fibreglass products. Most of them came in wanting batts. They left with cellulose once they understood what’s actually inside the bag.
Funny thing about insulation brand names. Steel wool doesn’t have any wool in it. Two-dollar gold coins aren’t made of gold. Earthwool® isn’t from a sheep. Gold Batts® aren’t actually gold (just a tint on them). I’m not knocking anyone’s product, just having a chuckle at the names. What matters is what’s inside the bag, and that’s where it gets interesting.
“I hope you realise by now that you are buying a service as much as a product.”Peter Johnson, Comfort Zone Insulation Team
I sell all three products. I fit batts every week for the people who want them, and the polyester ones are genuinely good. But I don’t have a dog in the fight between my own two products, so when I tell you the cellulose wins, it’s because after 6,000 roofs I’ve watched what each one does over time. If you want them lined up side by side, read cellulose vs fibreglass batts or the full 3-way comparison table.
Cellulose viewed straight up through the centre of a roof, one continuous blanket, no gaps anywhere. We make this in Tiaro; you can see how it’s made in our factory.
One-line version of the whole page: an R-rating only counts if there are no gaps, and batts always have gaps, so an R5 batt is not really an R5 in your roof.
Why Comfort Zone cellulose
The top 14 reasons I only recommend pumped-in cellulose.
The positive case, stacked. It's what I use in my own home, and every performance, health and environmental claim below links to a real, checkable source.
Seamless cover, no gaps
Pump-in means no gaps. That gives most homes about 40% higher effective R-value than batts after installation, because an R-rating only counts if there are no gaps. A small gap in a fridge seal stops it getting cold; the unavoidable gaps in batts ruin the result the same way. Full contact across every inch of the ceiling is the whole point.
Borax naturally keeps the bugs out
It's one of very few insulations treated with borax, and borax isn't a man-made chemical. It's a natural mineral salt, used in home cleaning remedies and laundry boosters for over a century, and about as toxic to people as table salt: don't eat the insulation, but unless you're worried about the kids grabbing the salt shaker off the dinner table, you don't need to worry about them touching this either. The ants, spiders, silverfish and other insects that infest a roof won't live in it, and being borate-treated it resists mould and fungal growth too, so cellulose roofs after 40 years are far cleaner than batt roofs. No insects means no food for rats, and no food for rats means no food for snakes.
Disinfectant & deodoriser
Boric acid is a natural disinfectant and deodoriser. A roof we put cellulose into 20 years ago smells nicer today than the day we installed it, because the insulation slowly neutralises whatever animal urine, droppings or general grime ends up in the cavity, instead of letting it sit there and stink. Roofs with batts don't do that. They just trap the smell.
Fire-retardant
Cellulose is treated with borax (a borax / boracic-acid mix), and Sustainability Victoria's Energy Smart Housing Manual states that treatment ensures that, if the material does ignite, the flame will not spread. Borax melts around 734°C, roughly 200° above the temperature of a house fire. Fibreglass batts melt away in a fire and leave your timber exposed, and the binders can give off poison gas. Cellulose has been shown to slow fire spread, and gives off only CO₂ and steam. See the full fire story in the #fire section below.
Recycled paper, low embedded energy
Cellulose is made from 75–85% recycled paper and takes a fraction of the energy to produce, roughly a tenth of the embodied energy of typical commercial insulation (peer-reviewed figures put cellulose at about 1–3 MJ/kg versus 11–45 MJ/kg for commercial insulation). It's also the insulation that can be vacuumed out and reused over and over.
No rats, no mice nesting
In 6,000 jobs I've never seen our correctly-installed cellulose get mice nesting in it. Comfort Zone cellulose we pumped 10+ years ago still looks new. I pull rat nests out of batt-insulated roofs every week. I have never pulled one out of a roof that was pumped with cellulose.
Hygroscopic, handles a roof leak
Unlike batts, cellulose is hygroscopic: it absorbs incidental moisture and then dries out, holding a small leak in one spot instead of letting it run across the ceiling. There's a bonus: on small-to-medium leaks the cellulose shows a discoloured patch directly below where the water came in, so when we do a roof inspection we can pinpoint it. Batts hide leaks because the water just flows under them into the rooms next door.
Helps stop ceiling mould, the full-contact way
The bigger reason cellulose helps with mould is full contact. Pumped-in cellulose sits flat against the plaster everywhere, with no gaps where heat from the roof cavity hits the cool ceiling and condenses. The Australian Government's yourhome guide ties these thermal bridges directly to condensation and mould. Batts always leave gaps where that temperature gradient drives moisture into the plaster; with every inch of the ceiling covered, the gradient is gone and the ceiling stays dry. The cellulose is borate-treated, which resists fungal growth too, but the thermal mechanism is the real reason.
Life-of-House guarantee, transferable
Our cellulose carries a written Comfort Zone Life-of-House Guarantee that you can pass on to whoever owns the home after you. We don't know of another insulation in Australia that carries this. And because we install to a specified density, it holds its thickness. It won't blow around or settle the way under-filled jobs do.
A strong sound insulator
Dense-packed cellulose fills the cavity completely and adds mass, so it's a strong sound insulator, especially for airborne noise like voices, TV, road noise and rain on a tin roof. I won't quote you a specific decibel figure without a sound report, because acoustic results depend on your whole ceiling or floor build-up, but the direction is clear, and the batt companies don't even rate their sound batts with an STC, they still quote R-value, which is the wrong metric for sound.
Resists air movement
Dense-packed cellulose resists air movement, so it cuts the draughts that whistle up through the gaps around cornices, downlights and power points. Hold a batt against a fan and air blows straight through it. Air leakage is a documented 15–25% of a home's winter heat loss in the Australian Government figures, so stopping it matters for your energy rating.
A real equipment barrier keeps the cowboys out
A proper cellulose install needs a real rig, about $100k of equipment. That barrier keeps the fly-by-night contractors out. Batts just need a trailer and a stepladder, both of which can be rented, and your house could be that installer's first job. Insulation hasn't been a licensed trade since 2006, so the equipment is one of the few things still standing between you and a cowboy.
Pipe lagging: hot water stays hot, cold stays cold
Pumped cellulose can be sprayed right over your hot and cold water pipework in the roof, so the hot pipes stay hot and the cold pipes stay cold. It's about the cheapest plumbing-efficiency upgrade you'll ever buy. Batts can't do this because they're not a seamless cover, just ask if you want it added.
The safest ingredients I know
It's just recycled paper, boric acid and borax. No ammonium sulfate, no asbestos, no formaldehyde, no sulphuric acid, no dyes, and no salt (that last bit's a joke). Cellulose is a plant fibre, not a glass fibre, and the Australian Government's CSIRO notes glass-fibre and rockwool can cause temporary skin, nose and eye irritation. Cellulose is gentler to handle, though, like any loose-fill, we wear dust masks while we're pumping it in.
Bonus reason
Comfort Zone cellulose is one of very few solutions that works on A-frame, flat, Super-6, raked or exposed-beam ceilings, and steel-frame homes. Most batt companies say it can’t be done, and we can do the hard roofs. Pumped in by a single operator instead of a crew dragging batts around, it goes in faster and safer.
Worried about what’s in it? It’s just recycled paper, boric acid and borax: no ammonium sulfate, no asbestos, no formaldehyde. Cellulose is recycled paper, and many a child has eaten the pages out of a book, so I’m not worried about a bit of it ending up in your water tank. Don’t eat the insulation, but unless you worry about the kids grabbing the salt shaker off the dinner table, you don’t need to worry about them touching this either.
Sources for the figures above: Australian Government: yourhome.gov.au (Insulation) for the gap, condensation, air-leakage and up-to-45% savings figures; Sustainability Victoria: Energy Smart Housing Manual for the fire-retardant statement; and CSIRO: Thermal Insulation for the handling and settling notes.
The fire story, a blowtorch on bare cellulose
Watch what doesn’t happen.
Cellulose is treated with a borax and boracic-acid mix during manufacture. The Australian state government’s Sustainability Victoria puts it plainly: that treatment “ensures that, if the material does ignite, the flame will not spread.” Borax itself melts around 734°C, roughly 200° above the temperature of a house fire.
Hold a blowtorch to a handful of bare cellulose and it chars and glows, but it won’t carry a flame, and it gives off only CO₂ and steam. Fibreglass batts melt away in a fire and leave your timber exposed, and the binders can give off poison gas. Cellulose has been shown to slow fire spread: in the widely-shared US “big burn” demonstration (1978), the cellulose-insulated structure took far longer to burn than the fibreglass one. That’s a demonstration you can watch, not a marketing line.
I won’t print a specific fire rating here unless I can show you our own AS 1530 test certificate, but the chemistry and the government’s own wording back what you see in the photo.
Source: Sustainability Victoria, Energy Smart Housing Manual (Fire safety) →
The smell test, 40 years on
Rats love batts. They leave cellulose alone.
The borax that keeps insects out is the start of the chain: insects won't live in it, so there's no food for rats, and no food for rats means no food for snakes. So a cellulose roof after 40 years is far cleaner than a batt roof: no urine, no droppings, no dirt to make it smell or look grim. The boric acid even works as a slow deodoriser, so a 20-year-old cellulose roof smells nicer today than the day we put it in.
And you don’t have to take my word for it. In independent US lab testing, termites couldn’t penetrate or survive in borate-treated cellulose (Mankowski & Grace, 2004), and borate-treated cellulose held off five separate mould species for more than four months (Herrera, 2005).
“I pull rat nests out of batt-insulated roofs every week. I have NEVER pulled a rat nest out of a roof that was pumped with cellulose.”
Plant-based & eco
The most environmentally-friendly insulation I know of.
People talk about “green” insulation and then point at super-heated spun rock or glass fibre. Cellulose is plant-based, recycled paper that started life as a tree pulling carbon out of the air.
I get asked all the time which insulation is the “eco” choice, and the honest answer surprises people. The marketing makes glass-fibre and rock-wool batts sound natural, but they’re made by super-heating spun rock or glass in a furnace that runs hot all day. Cellulose is the genuine plant-based product on the shelf: it’s recycled paper, and paper comes from trees that spent their lives pulling carbon out of the air. Turning that paper into insulation and pumping it into your ceiling keeps that carbon locked up in your roof rather than sending it back into the sky.
And here’s the part I like best: for once, the green choice and the comfort choice are the same choice. The most environmentally-friendly insulation I sell is also the best-performing one in your roof. You don’t have to trade a cooler, quieter house for a clear conscience. Here are the ten reasons cellulose is the real eco option, every one of them backed by a figure you can check rather than a leaf printed on a bag.
Seamless cellulose laid flush across the joists, recycled paper, locally made. We’re one of very few cellulose manufacturers left in Australia.
“Batts are made by super-heating spun rock or glass fibre. Cellulose is made by pulping recycled paper. I’m not looking for some rocks to stand on to cool my feet.”
- 1
About a tenth of the energy to produce
Cellulose takes roughly a tenth of the embodied energy of typical commercial insulation to manufacture. The peer-reviewed figures put cellulose at about 1–3 MJ for every kilogram produced, against 11–45 MJ/kg for commercial insulation, so even at the worst end it's a fraction of the energy. The reason is simple when you look at how each one is made. Batts are made by super-heating spun rock or glass fibre in a furnace; cellulose is made by pulping and shredding recycled paper. One of those processes is a furnace running hot all day, the other is closer to a giant paper shredder. Less energy in the factory means less carbon burned before the bag even leaves the building.
- 2
Made locally in small plants, not shipped across the world
Cellulose is made in small local plants rather than a handful of giant offshore factories, and we make ours right here in Queensland. We're one of the very few remaining cellulose-fibre insulation manufacturers in Australia, and the only one we know of still making it in Queensland. That keeps the transport footprint down: the paper comes from nearby, the bags go a short distance to your roof, and the money stays in the local economy and in local jobs. A product that's made down the road simply doesn't carry the freight emissions of one shipped halfway around the planet.
- 3
No virgin fibre: it's 75–85% recycled paper
Cellulose is made from 75–85% recycled paper, usually post-consumer waste newsprint that would otherwise head to landfill. There's no virgin glass being melted and no rock being quarried, crushed and spun to make it. The feedstock is the newspaper and cardboard that already exists. So instead of digging new material out of the ground, we're giving an old material a second, useful life in your ceiling, where it'll keep working for decades. That's the difference between recycling something and manufacturing something brand new from raw resources.
- 4
Reusable bags, used over and over
Our cellulose comes in heavy reusable poly bags that go back to the factory and get refilled hundreds of times over, not single-use plastic wrap that goes straight in the bin. Compare that with batts: I dump whole trailers of plastic batt wrappers every single month, job after job. With cellulose there's effectively zero waste plastic left over from your job, because the packaging is part of a loop that runs between the factory and the truck rather than ending up in a skip bin.
- 5
It needs trained installers, and that protects the result
You can't just hand cellulose to anyone with a stepladder and a ute. It needs the rig and trained installers who know how to pump it to the right density into every corner. That's an environmental win as much as a quality one: a job that's done right the first time doesn't get ripped out and re-done a few years later, which is exactly what sends batts to landfill early. The skill barrier that keeps the cowboys out also means the material you pay for actually stays in your roof doing its job, instead of becoming next decade's waste.
- 6
A century-old idea, invented in Canada
Cellulose insulation isn't some new, experimental product being trialled on your house. It was invented in Canada more than 100 years ago and has been keeping homes comfortable through brutal northern winters ever since. We've simply refined the way it's treated with borax and the way it's pumped in. When something has been proven across a century and a couple of continents, you're not the guinea pig. You're getting a mature, well-understood material with a long track record behind it.
- 7
It locks up carbon the tree captured
Paper is made from trees, and trees pull carbon dioxide out of the air as they grow. When that paper is turned into insulation and pumped into your ceiling, the carbon the tree captured is locked away in your roof for the life of the house instead of being released. So a cellulose ceiling is about as close to carbon-storing insulation as you'll find. It does the opposite of a furnace that burns fuel to spin rock. Think of the fire-walking trick where people stride across hot coals: carbon is a poor conductor of heat, and a roof full of paper-based carbon fibre behaves the same way, holding the heat back rather than passing it through.
- 8
Pumped-in means no gaps
Because it's pumped in rather than cut to fit, cellulose covers every inch of the ceiling with no gaps, and an efficient home is a greener home. The Australian Government estimates roof and ceiling insulation can cut heating and cooling costs by up to 45%, but you only get that result if the insulation is actually continuous. Batts leave gaps wherever they're cut to a bay or squeezed into a corner, and those gaps quietly bleed your heating and cooling energy. The seamless install is what turns the headline saving into a real one on your power bill.
- 9
Dense-pack stops the draughts
Because it's dense-packed, cellulose doesn't let draughts flow through all the little gaps in plaster cornices or around wall fittings. Power points, light fittings and the like in your walls let air flow up into the roof space, and with batts that air passes straight through, so your home leaks conditioned air all day. Cellulose resists that airflow and stops the draught at its source. Since air leakage is a documented 15–25% of a home's winter heat loss in the Australian Government's figures, sealing it off with a dense-packed material is a genuine efficiency gain, not a marketing one.
- 10
Better sound, and it works on steel frames
Dense-packed cellulose is a strong sound insulator and it can be pumped right over a steel frame, sitting hard against the steel where batts always leave gaps. Steel conducts heat readily (it's a thermal bridge), so on a steel-frame home full-contact cellulose makes a real difference that cut-to-fit batts simply can't match. You get a quieter, more comfortable home and a better-performing one for the same recycled, low-energy material. As I tell people who ask why I don't just throw in some cheap rock-fibre batts: I'm not looking for some rocks to stand on to cool my feet.
Put it together and you get insulation with a fraction of the embodied energy, no virgin fibre, reusable packaging and carbon locked away in your ceiling, which also happens to be the best-performing product I sell. The eco case and the comfort case point the same way for once.
Sources: Frontiers in Built Environment (2023) for the embodied-energy range and the 75–85% recycled-paper figure; yourhome.gov.au (Embodied energy) and yourhome.gov.au (Insulation) for the up-to-45% saving and air-leakage figures.
Before you buy batts, the R-value trap
“An R5 is an R5”, except it isn’t.
People assume R3.0 in one product equals R3.0 in another. It doesn’t. The rating is not the result. The install is. Even small gaps greatly reduce the effective R-value: Sustainability Victoria’s government nomogram shows installed R-value collapsing as the uninsulated percentage of the ceiling rises, and the same manual notes that leaving gaps of just 5% of the ceiling area can drop an R3.5 batt’s effective R-value to about R2.1, a loss of roughly 40%.
When batts get cut into all the different size bays in your roof and squeezed into the tight corners, most batt installers take short cuts, especially in tight, hot roofs. I’ve seen 100m of R3.0 batts stretched to cover 300m at R1.0, and the customer never noticed (he said the bloke was a real nice guy, too). Pumped-in cellulose can only be shorted one way: pump less in, and that’s measurable.
An R-rating only counts if there are no gaps, and batts always have gaps, so an R5 batt is not really an R5 in your roof.
The Australian climate zones. Here in South-East Queensland (Zone 2) the NCC minimum added ceiling insulation is about R2.5. We install to that, typically around R3.0.
Comfort Zone® Life-of-House Guarantee
Transferable to the next owner.
Our cellulose carries a written Life-of-House Guarantee that you can pass on to whoever owns the home after you, a real commitment in writing, not a slogan. We don’t know of another insulation in Australia that carries this. Because we install to a specified density, it holds its thickness rather than settling the way under-filled jobs do.
Batts get our Best Service Guarantee instead. Either way, a customer who has a problem fixed well refers us ten times more than one who never had a problem at all, so it’s firmly in our interest to make it right.
Honest answers
Cellulose questions I get asked most.
Why is cellulose better than fibreglass batts?+
Because it's pumped in as one seamless blanket with no gaps, where batts have to be cut to fit every bay and corner and always leave gaps. An R-rating only counts if there are no gaps, so a pumped-in cellulose ceiling delivers about 40% higher effective R-value than the same rating in batts. On top of that, cellulose is borax-treated so pests won't live in it and it has been shown to slow fire spread, it's hygroscopic so it handles a roof leak, and it carries a transferable Life-of-House Guarantee. After 6,000 roofs it's the only product I'd put in my own mother's house.
Is borax in cellulose insulation safe?+
Borax is a natural mineral salt, not a man-made chemical, that's been used in home cleaning and laundry products for over a century. It's about as toxic to people as table salt: don't go eating the insulation, but unless you'd worry about a child grabbing the salt shaker off the dinner table, you don't need to worry about them touching cellulose either. The borax is what keeps insects out, because they won't live in it, and being borate-treated it resists mould and fungal growth too, and it helps the cellulose resist fire.
Does pumped-in cellulose settle over time?+
The settling problems people hear about come from under-filled jobs, not from correctly dense-packed cellulose. CSIRO notes that, like any loose-fill, cellulose can settle if it's installed too lightly, which is exactly why we install to the product's specified settled density. In 6,000 jobs I've never seen our correctly-installed cellulose settle, blow around or get mice nesting in it, and we back it with a written guarantee rather than a physics promise.
Is cellulose fire-retardant?+
Yes. Sustainability Victoria's Energy Smart Housing Manual states that cellulose fibre must be treated with a borax / boracic-acid fire retardant, and that this treatment ensures that, if the material does ignite, the flame will not spread. Borax melts around 734°C, roughly 200° above house-fire temperature. Hold a blowtorch to a handful of bare cellulose and it chars and glows but won't carry a flame, and it gives off only CO₂ and steam, where fibreglass melts away and its binders can give off poison gas.
Is cellulose more expensive than batts?+
It's a bit dearer than batts, yes, but for a little extra cost you get a much better-performing insulation and a far better result over the life of your house. You're buying a service as much as a product: a seamless install, no gaps, pest and fire resistance, and a transferable guarantee. If you can afford a bit extra now, cellulose is the only insulation I recommend you actually use.
Can cellulose go in any roof?+
It goes in roofs most batt companies say can't be done: A-frame, flat, very low-pitch, raked, exposed-beam and Super-6 roofs, plus steel-frame homes where it can be pumped right over the steel. The reason other companies say it can't be done is usually that you're talking to a sales rep, not an installer. We've got the rig and the training to do the hard ones, and there's a #plant-based environmental bonus to doing the job right once.
Ready to put cellulose in your roof?
You’ve seen the fourteen reasons I stand by it, the fire test, the eco case, and why an R5 batt isn’t really an R5. Whatever you decide, I’ll give you an honest quote and an honest answer. Fill in the simple online form and you’ll have a detailed quote within 48 hours for most houses.
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