Materials and R-value
Mineral Wool / Rockwool
Spun stone fibre. Chosen where fire resistance or sound matter as much as the thermal value.
Thermal resistance
What the R-value actually is
Range
R-3.0 to R-3.8 per inch
Design value used
R-3.0
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 format — and the difference between formats is large enough to matter.
This range is for BLOWN mineral wool, and it comes from Natural Resources Canada. Rigid mineral wool board is a different product with a different number, published by its manufacturers rather than by an independent body — ask for the specific product data sheet rather than relying on a figure quoted second-hand.
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
- Assemblies where fire resistance is part of the objective
- Party walls, stairwells and anywhere airborne sound is a complaint
Not the right choice when
- Situations where the only objective is thermal value per dollar — glass fibre reaches a similar number for less
Beyond the number
Moisture, fire and sound
Moisture
Stone fibre does not feed mould and sheds water rather than holding it, though a wet assembly is still a wet assembly.
Fire
Resists melting up to 1177 °C (2150 °F). Source: NAIMA Canada. This is the property it is usually specified for.
Sound
Johns Manville publishes NRC 0.95 to 1.05 and STC 45 to 52 for its Minwool product line. Those are that manufacturer's figures for that product, not a universal value for mineral wool, and another product will not necessarily match them.
Services that use it
Problems it helps correct
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
Is mineral wool worth the extra cost in an attic?
For thermal value alone, usually not — blown glass fibre or cellulose reaches a similar number for less. Where it earns its cost is in an assembly where fire resistance or sound is part of what you are buying.
Is blown mineral wool the same product as the rigid board?
No, and the numbers are not interchangeable. The range shown above is for the blown format and comes from Natural Resources Canada. Rigid mineral wool board is a different product whose figures are published by its manufacturers, so ask for the data sheet of the specific board being proposed rather than relying on a number quoted second-hand.
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.