Open-Cell vs Closed-Cell Spray Foam — Ontario Guide

The technical differences come from cell structure. Closed-cell has tiny sealed cells holding gas, which gives it a high R-value and water resistance. Open-cell has connected cells filled with air, which makes it lower in R-value, more flexible, and sound-absorbing.

The behaviour of each foam in an Ontario assembly follows directly from those properties.

Open-cell is the right pick in these situations:

1. above-grade walls in a heated, conditioned space, including interior partitions and exterior 2x6 walls in homes with proper exterior vapour control
2. attics with good ventilation where you want sound dampening from the roof
3. sound-sensitive partitions such as bedrooms, home theatres, and music rooms, where the cellular structure helps with STC
4. budget-constrained projects where cavity depth alone reaches the target R-value.

A 2x6 wall reaches R-22 with open-cell at full depth, which meets the OBC Climate Zone 6 minimum for above-grade walls.

The cost-per-R-value math favours open-cell when the cavity is deep enough to hit code minimums without compression.

Closed-cell is the only correct choice in these situations:

1. below-grade walls, since basement walls need vapour control against the foundation and closed-cell handles incidental moisture without growing mould
2. rim joists and band joists, which are high air-leakage zones that benefit from a thin layer of high-R-value foam
3. shallow cavities, since a 2x4 wall cannot reach R-22 with open-cell in 3.5"
4. flat roofs and unvented attics, where humid Ontario summers call for vapour control on the warm side
5. any assembly exposed to potential bulk water, such as basement rim joists, cathedral ceilings, and exposed roof undersides.

The higher cost is offset by better long-term durability and the elimination of separate vapour barrier products.

Cost differences widen as you scale up. A typical 1,000 sq ft basement wall area insulated to R-20 minimum with closed-cell at 3" runs $4,800–$8,500 in 2026.

The same area with open-cell cannot reach R-20 in a standard 2x4 stud cavity. It would need roughly 5.5" of thickness, which does not fit.

OBC SB-12 sets minimum R-values per building element in Climate Zone 6: R-22 for above-grade walls, R-20 for basement walls, and R-60 for attics. Both foams meet the spec when sized correctly.

The federal Canada Greener Homes Grant stopped accepting new applications in 2024. Ontario homeowners should check current Home Efficiency Rebate and Enbridge Gas incentives, which vary by program year and require pre- and post-retrofit EnerGuide evaluations. Confirm eligibility and installed R-value requirements before you book work.

For air leakage control under SB-12 prescriptive paths, both foams are recognized air barriers, but only closed-cell is a vapour barrier on its own. Pairing the two in one assembly, with closed-cell on the cold side and open-cell as a topup, is increasingly common in cathedral ceilings and high-performance walls. Specify that approach with a building science consultant or experienced designer to avoid trapping moisture between layers.