Materials and R-value
Blown-in Cellulose
Treated recycled paper fibre, blown in. It packs more tightly around obstructions than glass fibre, which is why it is chosen for attics with a lot in the way.
Thermal resistance
What the R-value actually is
Range
R-3.0 to R-3.8 per inch
Design value used
R-3.6
Natural Resources Canada, Keeping the Heat In, Section 3. Read the source. Consulted August 25, 2026.
This is a range, not a single number, and the range is the honest form. The value you actually get varies with installed density, the depth after settling, and the product formulation.
The Natural Resources Canada value is already a settled-thickness value, so it is not reduced again for settling.
R-value per inch is one property among several. Moisture behaviour, fire and sound are below, and the assembly decides which of them matters most. Compare the six on the Materials & R-Value guide.
Where it fits, and where it does not
Appropriate for
- Attics crowded with framing, wiring and obstructions, where following the geometry matters
- Situations where limiting small coverage gaps is the main objective
Not the right choice when
- Attics with active moisture entry — it is an organic material and it holds water
- Where the depth cannot be built up enough to allow for settling
Beyond the number
Moisture, fire and sound
Moisture
Organic fibre. It takes on moisture in a way glass fibre does not, which makes an unresolved leak or condensation source a reason to correct the source first rather than a detail to note.
Fire
Naturally combustible without treatment; treated with borate flame retardants at roughly 20% of its weight. Source: NAIMA Canada.
Sound
Dense loose fill dampens airborne sound better than a light one, but no independent figure is published here.
Services that use it
Problems it helps correct
Deciding, rather than specifying
This page is the technical side — the numbers, the limits and where the material is the wrong choice. If you are weighing it up for your own house, the guide covers that:
About this material
Questions we get on this one.
Tap a question and the answer comes back. Anything specific to your project, we sort out on the call.
Eco-Therma
Usually replies the same day
How much does cellulose settle?
NAIMA Canada puts settling in attics at as much as one fifth of the installed depth. That is why it goes in above the target depth rather than exactly at it — the depth that matters is the one it holds in five years, not the one on the day it goes in.
Is the fire treatment permanent?
The borate treatment is part of the material rather than a coating on it. What it does not survive is soaking: material that has been repeatedly wet is replaced rather than dried in place.
The attic decides which material, not the price list.
Send the address and roughly how big the attic is, and we come back with a range and the material it is built on.