Materials and R-value
Closed-Cell Spray Foam
The densest option, and the only one that is insulation, air barrier and vapour barrier at once. Also the one whose number is most often quoted wrong.
Thermal resistance
What the R-value actually is
Range
R-5.2 to R-6.5 per inch
Design value used
R-6.0
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 the product, the thickness, and — uniquely among these six — how long ago it was installed.
Natural Resources Canada deliberately CAPS the design value at R-6.0 per inch because of long-term thermal resistance testing, even though initial measurements reach R-6.5. The blowing agent diffuses out of the foam over time and is replaced by air. The Canadian standard covering this measurement is CAN/ULC-S770. This is the clearest example on the site of why a single universal number would be misleading.
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
- Cold-climate assemblies where an air barrier and a vapour barrier are both required
- Unvented roof assemblies and irregular structure interrupted by services
- Where condensation control on a cold surface is part of the objective
Not the right choice when
- Assemblies designed to dry inward, which it would prevent
- Where the roof is being rebuilt from above and board systems are the appropriate approach
Beyond the number
Moisture, fire and sound
Moisture
Acts as a vapour barrier at sufficient thickness. That is the reason to choose it and the reason to be careful with it: an assembly that needed to dry in that direction no longer can.
Fire
Requires a thermal or ignition barrier as the assembly calls for.
Sound
Its density makes it a poorer sound absorber than open-cell, which is the opposite of what its higher thermal number suggests.
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
Does closed-cell spray foam lose R-value as it ages?
Yes, and it is not a defect — it is why the design value is lower than the value measured on installation day. The blowing agent diffuses out of the foam and is replaced by air. Natural Resources Canada caps the design value at R-6.0 per inch for exactly this reason. Anyone quoting a precise percentage of loss should be asked for the study it came from.
It has the highest number. Why is it not always the answer?
Because per-inch value is one property among several. It is also a vapour barrier, which is what you want in some assemblies and a problem in others, and it costs more per inch than anything else on this list. The assembly decides.
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.