Insulation types and R-value

Every type of home insulation does the same job: it divides the still air inside a wall, ceiling or floor into small pockets so heat moves through more slowly. The measure of how well a material resists that heat flow is its R-value (or RSI in metric). A higher number means more resistance per unit of thickness. What separates the materials is not the principle but how they are installed, how they behave when they get wet, and how much resistance they deliver per inch.

Reading an R-value before you buy

R-value is additive within an assembly, so a wall's total resistance is the sum of its layers. It is also a rated property measured under ideal conditions. In a real wall, air movement through gaps undermines that rating: published Canadian guidance notes that air leakage can reduce the effective performance of an assembly well below the labelled R-value, which is why air sealing is treated as a prerequisite rather than an afterthought.

The per-inch figures above are drawn from Natural Resources Canada's Keeping the Heat In material tables. Two materials with the same rated R-value are not always interchangeable: a board that performs well above grade may lose resistance in cold conditions, and a foam suitable for a rim joist may be the wrong choice spread across a whole wall.

The four families in practice

Batt and roll

Fibreglass and mineral wool batts are the most familiar option for open stud and joist cavities. They are inexpensive and quick to fit, but they only perform when they fill the cavity completely — compressed batts, gaps around wiring, and unfilled corners all reduce the result. Mineral wool adds fire and moisture tolerance at a higher cost.

Loose-fill

Blown cellulose or fibreglass settles into spaces that batts cannot reach neatly, which makes it a common attic choice. It conforms around obstructions but needs a clear depth marker and proper density to hit its target R-value, and it relies on an intact air barrier underneath to avoid wind-washing.

Rigid board

XPS, EPS and polyiso boards provide a continuous layer of insulation, most usefully on the exterior of a wall where they break the thermal bridge formed by the studs. Continuous exterior board is increasingly paired with cavity insulation to meet stricter climate-zone targets.

Spray foam

Closed-cell spray polyurethane delivers high resistance per inch and can act as its own air and vapour control layer, which makes it useful at rim joists and in irregular cavities. It is the most expensive option and is applied by trade installers rather than as a homeowner task.

Matching material to location

• Attic: loose-fill is economical over a large flat area, provided the ceiling air barrier is intact first.
• Above-grade walls: batt in the cavity, often with continuous rigid board outside to cut thermal bridging.
• Basement and below grade: moisture-tolerant rigid board or closed-cell foam, with attention to the full foundation height.
• Rim joist: a small, leaky area where closed-cell spray foam seals and insulates in one step.

Where this connects

Choosing a material is only the first decision. How the assembly handles air and moisture — covered in air and vapour barriers — determines whether the rated R-value survives in service. Sealing the openings that bypass the insulation entirely is covered in window sealing and weatherproofing.