Rigid Foam vs Spray Foam — Ontario Insulation Guide

Rigid foam comes in three common products: XPS (extruded polystyrene, blue or pink), EPS (expanded polystyrene, white beadboard), and polyiso (yellow, foil-faced). Spray foam comes in two: open-cell (0.5 lb) and closed-cell (2 lb).

Note that polyiso loses some R-value in cold temperatures, so its rated value drops on exterior applications during Ontario winters. Design to the long-term thermal resistance (LTTR) listed for each product.

Rigid foam is the better choice in these cases:

1. continuous exterior insulation over framing, where XPS or polyiso boards over wall sheathing reduce thermal bridging through studs and are increasingly specified for high-performance Ontario builds (Net Zero, Passive House, R-2000) and for meeting the tiered energy-efficiency targets in the 2024 Ontario Building Code
2. below-grade foundation exterior, where XPS bonded to the outside of the foundation wall is the standard basement insulation method
3. flat roof above-deck, where polyiso is the dominant commercial insulation
4. DIY budget retrofits, since an experienced homeowner can screw and tape rigid foam
5. under concrete slabs, where XPS is the only insulation rated for direct concrete contact in below-grade applications.

For continuous exterior insulation over framing, rigid foam is the only practical option.

Spray foam wins in these cases:

1. irregular cavities, such as basement walls with stone foundations, rim joists, attic transitions, and cathedral ceilings
2. air sealing as the priority, since closed-cell foam seals every gap, fastener hole, and crack
3. tight cavities, where a 2x4 wall reaching R-22 needs closed-cell foam at depth and rigid board cannot fit
4. retrofits with limited access, since small crawl spaces and rim joists are easier to spray than to cut and fit with board
5. one-pass insulation, air barrier, and vapour barrier, which removes the separate poly sheet and tape labour.

For irregular cavities and air sealing, spray foam beats rigid foam on labour even though material cost runs higher.

Rigid foam costs less on flat, regular surfaces. Spray foam catches up on irregular cavities, where the labour to fit rigid board accurately exceeds the spray premium. Figures below reflect 2026 GTA pricing, which has risen roughly 5 to 8 percent since 2024 on material and labour costs.

Many high-performance Ontario builds use both. A typical approach places closed-cell spray foam against the structural element (interior of a basement wall, underside of a roof deck) for air and vapour control, then adds rigid foam continuous over framing to cut thermal bridging. This pairs spray foam's air sealing with rigid foam's continuous coverage.

For basement walls, the standard approach in GTA new builds is 2 to 3 inches of closed-cell spray foam directly against the concrete (vapour control and air seal), then a 2x4 stud wall with batt fill for a total cavity of R-22 or better. This removes separate vapour barrier work and gives basement walls that perform like above-grade walls.

Check current spray foam product approvals and installer certification with your municipality before booking work, since the 2024 Ontario Building Code updated several insulation and air-tightness provisions.