Materials and R-value
Open-Cell Spray Foam
Foam that expands to fill the shape it is sprayed into and stays vapour-permeable. Air barrier and insulation in one operation.
Thermal resistance
What the R-value actually is
Range
R-3.6 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 the thickness applied and the manufacturer's formulation.
A narrow range compared with closed-cell, because the blowing agent is water and there is far less long-term drift to account for.
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
- Irregular assemblies where board and batt cannot be fitted cleanly
- Where the air seal is the main objective and the assembly is designed to let vapour pass
Not the right choice when
- Where the assembly requires a vapour barrier and no other measure is planned
- Anywhere the existing material has to come out first — that is a removal scope
Beyond the number
Moisture, fire and sound
Moisture
Vapour-permeable, unlike closed-cell. Whether that is an advantage or a problem depends entirely on which way the assembly is designed to dry, which is a question about the building rather than about the foam.
Fire
Requires a thermal or ignition barrier as the assembly calls for. The requirement comes from the assembly and the authority having jurisdiction, not from us.
Sound
The open cell structure absorbs airborne sound better than closed-cell, though 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
What is the actual difference between open and closed cell?
Open-cell is lighter, less expensive per inch, and lets vapour through. Closed-cell is denser, reaches a higher value per inch, and acts as a vapour barrier. The choice is decided by how the assembly is meant to dry, not by which number is bigger.
Can open-cell foam be left exposed once it is sprayed?
Generally no. A thermal or ignition barrier is normally required over it, and what qualifies is set by the assembly and the authority having jurisdiction rather than by the foam itself. That covering is part of the scope and part of the cost, so it belongs in the quote rather than as a surprise afterwards.
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.