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Insulation materials · Cellulose
Cellulose: the recycled paper that keeps the home cool in summer
The bio-based insulant par excellence. Made from shredded recycled newspaper treated with borate salts, cellulose insulates in winter just as well as conventional wools — but above all, its high thermal capacity slows summer heat like no other common insulant. Eco-friendly, with very low embodied energy, and strong on acoustics.
- λ 0.038–0.042
- W/m·K
- ~10–12 h
- of thermal lag
- Low embodied energy
- locally bio-based
85% recycled paperbio-based insulant
Summer comfortthermal lag ~10–12 h
Technical specs
What cellulose is really worth
The figures that matter for a bio-based insulant installed by our teams. Concrete benchmarks, no greenwashing.
- Conductivity λ 0.038–0.042 W/m·K
On a par with good mineral wools. To reach R = 6 m²K/W in an attic (the grants target), you need about 24 to 26 cm of blown cellulose — a thickness easy to achieve in an unconverted attic.
- Summer comfort ~10–12 h thermal lag
This is its major asset. Its high thermal capacity (dense material) strongly slows heat: under a roof, the outdoor heat peak only reaches the inside late in the evening, heavily dampened. Far more effective than light wool against overheating.
- Hygrometric regulation Hygroscopic
Cellulose absorbs then releases water vapour without losing its qualities: it buffers the wall’s moisture and improves comfort. A well-controlled installation (with a suitable vapour-check membrane) remains essential.
- Acoustics Very good
Its mass and fibrous structure make it an excellent sound insulant: airborne noise, impact noise and rain noise on the roof are clearly dampened, better than light insulants.
- Fire behaviour Euroclass B–C
The borate salts make the cellulose flame-retardant and antifungal (protection against mould and rodents). It doesn’t ignite but chars slowly; its fire class stays below that of rock wool (A1).
- Ecology / embodied energy Very low
Made from recycled paper, lightly processed and often produced locally: its embodied energy is among the lowest of any insulant. A leading choice for an eco-conscious approach and a durable renovation.
* Indicative values for common-range loose-fill cellulose. The thermal lag depends on the installed density and thickness. Exact performance confirmed during the survey.
Full transparency
Cellulose: strengths & limits
No insulant is perfect everywhere. Here, honestly, is where cellulose excels and where you need to be careful.
Where it shines
- Exceptional summer comfortIts strong thermal lag keeps attics cool in summer, where light wools give out.
- Eco-friendly bio-based insulantRecycled paper, low embodied energy: the benchmark for a durable renovation.
- Regulates moistureA hygroscopic material that buffers water vapour and keeps the wall healthy.
- Excellent acousticsIts mass strongly dampens airborne, impact and rain noise.
What you should know
- Settling riskInsufficient installed density causes blown cellulose to settle: it demands a serious, certified installer.
- Sensitive to permanent moistureWater damage or a prolonged leak degrades its qualities: roof watertightness and a vapour-check membrane are essential.
- Lower fire classFlame-retardant but less fire-resistant than rock wool (A1), to consider when installing near heat sources.
- Technical installationBlowing and especially dense injection into closed cavities require equipment and know-how — rarely a DIY job.
Which project
Is cellulose right for you?
It comes into its own whenever you’re after summer comfort, an eco-conscious approach and good acoustic performance. A few cases where it shines:
-
Unconverted attics
The ideal playground: cellulose is blown loose over the attic floor, in thick layers, quickly and with no cutting. Excellent performance-to-price ratio.
-
Walls & timber-frame cavities
Injected at high density into closed cavities (frame walls, slopes), cellulose fills every cavity with no thermal bridge and limits settling.
-
Roof & summer comfort
Under a sun-exposed roof, its thermal lag transforms the comfort of upstairs bedrooms in a heatwave, where wool alone gives out.
Need a different insulant logic?
For the best performance-to-price ratio and an A1 fire class, mineral wool remains a safe bet. And for the lowest lambda in slim thickness, look at PUR / PIR.
Glissez la poignée pour comparer
Real case · detached house, Namur
Loft bedrooms finally liveable in the height of a heatwave
Under a south-facing roof, the upstairs bedrooms became unliveable in summer. We injected cellulose at high density into the slopes and blew the unconverted attic, reaching R = 6. The result: a thermal lag that pushes the heat peak into the evening and a lighter heating bill in winter.
- R 6m²K/W in the roof
- ~11 hof summer thermal lag
- −4 °Cupstairs in a heatwave
Customer reviews
They chose wendows
4.5/5 · 2verified reviews
« Insufflation des murs creux, rapide et sans dégât. La prime régionale a couvert une bonne part. Maison nettement moins froide. »
David K.Huy
Compare the options
Cellulose, or another insulant?
Cellulose wins on summer comfort and ecology. Compare it point by point with mineral wool and PUR/PIR, then open the material that interests you.
| Critère | CelluloseVous êtes ici | Mineral woolVoir la gamme → | PUR / PIRVoir la gamme → |
|---|---|---|---|
| Conductivity λ | 0.038–0.042 | 0.032–0.040 | 0.022–0.028 |
| Thermal lag / summer comfort | Excellent (~10–12 h) | Low to medium | Low |
| Ecology / embodied energy | Bio-based, very low | Average | High (petrochemicals) |
| Fire behaviour | Euroclass B–C | A1 non-combustible | Combustible (B–E) |
| Moisture behaviour | Hygroscopic, regulates | Sensitive if unprotected | Insensitive (closed) |
| Indicative price | €€ — intermediate | The gentlest | €€€ — higher |
| Ideal for | Attics, summer comfort, eco | Tight budget, fire safety | Slim thickness, floors |
Indicative benchmarks for common ranges. The right insulant depends on the wall and the goal — we fine-tune it together during the survey.
- overview
All the materials
Compare cellulose, wools, PUR/PIR and bio-based insulants at a glance, to suit your project and budget.
See all the materials → - vs cellulose
Mineral wool
The best performance-to-price ratio with an A1 non-combustible fire class. The safe bet for attics and walls.
Compare with wool → - vs cellulose
PUR / PIR
The lowest lambda for the slimmest thickness. Ideal where every centimetre counts (floors, flat roofs).
Discover PUR/PIR → - to combine
Attic insulation
Unconverted or converted attics: blown cellulose gives its best here. The most cost-effective job.
See attic insulation → - to combine
Roof slopes
Injected at high density into the slope cavities, cellulose insulates with no thermal bridge and takes care of summer comfort.
Insulate the slopes → - ↑ category
All about insulation
An overview of our insulation solutions in Belgium: attics, walls, roof, floors, materials, installation and grants.
Back to the insulation guide →
Indicative 2026 pricing
How much does cellulose cost?
The price depends on the target thickness (R), the technique (blowing or injection) and site access. Here are some benchmarks for installed cellulose, with grants deductible afterwards.
See the detailed insulation price list →* Indicative ranges per m² of cellulose installed, excluding specific set-ups. A costed estimate is provided with your free quote.
- Blowing in attics €20–30/m²loose-fill, R = 6, supplied & installed
- Injection in cavities €30–45/m²high density, walls / slopes
- Renovation grant up to 35%of the amount, depending on your income
- Reduced VAT 6%for renovation (home > 10 years old)
Cellulose FAQ
Your questions about cellulose
Does cellulose insulate as well as glass wool? +
In winter, yes: its lambda (0.038–0.042) sits at the level of good mineral wools. But it’s above all in summer that it stands out: its high thermal capacity creates a thermal lag of around 10 to 12 hours, which slows heat far better than light wool and keeps attics cool.
What is thermal lag and why does it matter? +
Thermal lag is the time it takes outdoor heat to cross the insulant. With cellulose, the afternoon heat peak only reaches the inside late in the evening, heavily dampened. That’s what makes loft bedrooms liveable in a heatwave, where wool alone quickly gives out.
Is cellulose at risk of settling? +
Settling only happens if the installed density is insufficient. Installed at the right density by a certified applicator (blowing in attics, high-density injection in cavities), cellulose stays stable over time. That’s why the choice of installer is decisive.
Is cellulose treated against fire and pests? +
Yes. It is treated with borate salts, which make it flame-retardant (it doesn’t ignite, it chars slowly) and antifungal: it resists mould and doesn’t attract rodents or insects. Its fire class nevertheless stays below that of rock wool.
Is it a genuinely eco-friendly insulant? +
It’s one of the most virtuous bio-based insulants: made from recycled paper, lightly processed and often produced locally, it has one of the lowest embodied energies on the market. A consistent choice for a durable renovation and an eco-conscious approach.
What grants are available for cellulose insulation? +
Grants depend on the performance achieved (resistance R), not on the material: attic insulation at R = 6 qualifies, depending on your region and income, for a renovation grant and the 6% VAT rate for homes over ten years old. We handle the paperwork for you.
Get your free cellulose insulation quote within 48h
Free on-site survey, grants calculated, a single point of contact. Describe your project in under a minute.
- Free and no obligation
- Grants & 6% VAT handled for you
- Installed by certified applicators