Compare · Cellulose vs spray foam
Cellulose vs spray foam: higher R isn’t the whole story.
Spray foam has a higher R-per-inch. But pump-in cellulose reaches the same total R with no gaps, lifts back out if you need it, uses no isocyanates, is recyclable at about a tenth the embodied energy, and carries a transferable life-of-house guarantee.
I’m Peter Johnson. I don’t sell spray foam, so this isn’t my product against yours. It’s 40 years and 6,000 roofs telling you what I’d put in my own home, and why. I’ll give foam its due first, then show you where cellulose wins, with every figure cited to a real source.
Seamless, and reversible
no gaps, vacuums back out, recyclable
Credit where it’s due
First, the case FOR spray foam.
Closed-cell spray foam has a higher R-value per inch than just about any other insulation, and it expands to fill, so a good operator can get a seamless result. If you truly can’t fit the depth (a tight cathedral void, a thin wall cavity) that R-per-inch is a real advantage. I won’t pretend otherwise.
I’ve been in a lot of roofs, and I’m not here to rubbish a product I don’t sell to sell you one I do. Spray foam is a legitimate insulation with one clear strength: it packs more R into less thickness than anything else on the shelf. So if you came here reading about foam’s headline number, that number is true. The question is whether it’s the number that decides the job.
For most Australian ceilings and roofs, it isn’t. You’re not short of space up there, so the one thing foam is best at, squeezing R into a thin layer, is the one thing you don’t need. We just pump the cellulose thicker to reach the R-value your SE-QLD climate zone actually calls for. And the moment you put foam in, you’re also taking on everything else that comes with it. That’s where the rest of this page comes in. If you’re weighing foam under a floor rather than in a ceiling, here’s the underfloor comparison, where the moisture story matters even more.
The one-line version
Foam wins R-per-inch. Cellulose wins everywhere a homeowner actually feels it: gaps, removability, what it’s made of, the environment, and what you’re left holding.
And R-per-inch only matters when space is tight. In a roof, it isn’t.
Where cellulose wins
Four places foam’s headline R-value can’t help you.
None of these are about beating foam on its strongest number. They're about the things that decide whether you're happy with your roof in ten years' time.
With pump-in, the R-per-inch race doesn't matter
Foam's headline is R-per-inch, and it's true, but it only matters when you're short of space. In a ceiling you're not. We just pump the cellulose thicker to reach the total R-value you want, as one seamless blanket with no gaps. An R-rating only counts if there are no gaps anyway, so once both products are in with no gaps, you're comparing total R against total R, and there I can simply add more depth for a fraction of foam's cost.
It lifts back out. Foam is forever
Cellulose can be vacuumed straight back out if you renovate, re-wire, add downlights or replace a ceiling, and it can be reused. Cured spray foam bonds to the timber, pipes and wiring it was sprayed over; Australian installers describe removing it as complex, labour-intensive and costly, often needing damaged timbers repaired afterwards. With foam, what goes on stays on, so you want to be very sure before you commit your roof to it.
No isocyanates: recycled paper, not a chemical reaction in your roof
Spray polyurethane foam is made by reacting isocyanates on site, and SafeWork NSW lists isocyanates as one of the leading causes of occupational asthma in Australia. Occupants are typically asked to leave the home while it sprays and cures, and cheap or badly-mixed foam can off-gas VOCs for days. The fair caveat: fully cured, correctly-installed foam is largely inert. Cellulose carries none of that: it's recycled paper and borax, inert from day one, though like any loose-fill we wear dust masks while we pump it.
Recyclable, and about a tenth of the embodied energy
Cellulose is made from 75–85% recycled paper and takes roughly a tenth of the embodied energy of typical commercial insulation to produce: the peer-reviewed figures put it at about 1–3 MJ/kg against 11–45 MJ/kg for commercial insulation. It can be vacuumed out and reused over and over. Spray foam is a petrochemical product blown on site that stays put for the life of the building. If the green case matters to you, recycled paper fibre wins it comfortably.
Reason five, and it’s in writing
A transferable guarantee, plus fire you can watch.
Our cellulose carries a written Comfort Zone Life-of-House Guarantee that you can pass on to whoever owns the home after you, and we don’t know of another insulation in Australia that carries this. And the borax treatment does real work: Sustainability Victoria’s Energy Smart Housing Manual states that treatment ensures that, if the material does ignite, the flame will not spread. Hold a blowtorch to a handful and it chars and glows but won’t carry a flame, giving off only CO₂ and steam.
Sources for the figures above: Frontiers in Built Environment (2023) for the embodied-energy range and the 75–85% recycled-paper figure; SafeWork NSW for isocyanates as a leading cause of occupational asthma; and Sustainability Victoria, Energy Smart Housing Manual for the borax fire-retardant statement.
Side by side
Cellulose vs spray foam, axis by axis.
Foam wins one row outright. Read down the rest before you let that one row decide your roof.
Pump-in cellulose recycled paper, borax-treated ★ What I’d use | Spray foam closed-cell polyurethane | |
|---|---|---|
| R-value per inch | Lower per inch, but in a ceiling you've got the depth to pump it thicker, so you reach the same total R-value with no gaps. | Higher R-per-inch: the one axis foam wins outright. It only matters where space is tight, which a roof space rarely is. better |
| Gaps after install | Pumped in as one seamless blanket: no joins, no cut edges, full contact across every inch of the ceiling. better | Sprayed and expands to fill, also seamless when done well, but only as good as the operator and the substrate on the day. |
| Can you remove it later? | Yes: it vacuums straight back out for a renovation, re-wire or new ceiling, and can be reused. better | Not easily. It bonds to the timber, pipes and wiring; removal is complex, costly and can damage the structure. |
| What it's made of | 75–85% recycled paper treated with borax, a plant fibre, no isocyanates, gentle to handle (we wear dust masks pumping it). better | Polyurethane made by reacting isocyanates on site, a leading cause of occupational asthma in Australia during spraying and cure. |
| Embodied energy | Roughly a tenth of the embodied energy of typical commercial insulation (about 1–3 MJ/kg, peer-reviewed). better | A petrochemical product manufactured and blown on site, with far higher embodied energy than recycled paper fibre. |
| What you're left holding | A transferable, written Life-of-House Guarantee you can pass to the next owner, and an option to change it later. better | Whatever the installer warranted, plus a permanent fixture. If a concern ever bites, you own it, not the operator who's long gone. |
Want the full positive case for cellulose, the 14 reasons, the fire story and the eco list? Read why cellulose is the only product I’d put in my own home.
Straight answers
Cellulose vs spray foam, the questions I get asked most.
Doesn't spray foam have a higher R-value than cellulose?+
Per inch, yes: closed-cell spray foam has a higher R-value than cellulose. But R-per-inch only matters when you're short of space, and a ceiling cavity rarely is. We simply pump cellulose thicker to reach the same total R-value you'd get from foam, as one seamless blanket with no gaps. An R-rating only counts if there are no gaps in the first place, so once both are installed properly you're comparing total R against total R, and I can add depth for a fraction of foam's cost.
Can you remove spray foam if I change my mind later?+
Not easily. Once it cures, spray foam bonds to the joists, pipes and wiring it was sprayed over. Australian installers describe removing it as complex, labour-intensive and costly, often needing damaged timbers repaired or replaced afterwards. Cellulose is the opposite: it vacuums straight back out for a renovation, re-wire or new ceiling, and it can be reused. That reversibility is one of the biggest reasons I'd put cellulose in my own home before foam.
Is spray foam off-gassing something I should worry about?+
The real, documented risk is during spraying and curing, not for years afterwards. Spray polyurethane foam is made by reacting isocyanates on site, and SafeWork NSW lists isocyanates as one of the leading causes of occupational asthma in Australia. Occupants are typically asked to leave the home while it cures, and cheap or badly-mixed foam can release VOCs for days. The fair caveat: fully cured, correctly-installed foam is largely inert. Cellulose carries none of that: it's recycled paper and borax, inert from day one.
Is cellulose better than spray foam for the environment?+
On embodied energy and recyclability, yes. Cellulose is made from 75–85% recycled paper and takes roughly a tenth of the embodied energy of typical commercial insulation: peer-reviewed figures put it at about 1–3 MJ/kg versus 11–45 MJ/kg. It can be vacuumed out and reused. Spray foam is a petrochemical product blown on site that stays for the life of the building. If the green case matters to you, recycled paper fibre wins it comfortably.
What about spray foam under my floor instead of polyester?+
That's a different question, and under a floor in our humid climate I wouldn't use foam either. Closed-cell foam seals the underside of your floorboards airtight, which can trap moisture against the timber and drive hidden rot, where polyester stays vapour-open and lifts straight out. I've laid out the full underfloor comparison on its own page so you can see the moisture, removal and cost case spelt out.
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