What Spray Foam Is.
Two materials, two standards, two very different sets of properties. Closed-cell medium-density foam is written to CAN/ULC-S705.1; open-cell light-density foam is written to CAN/ULC-S712.1. Almost every argument about spray foam is really an argument about which one is being discussed.
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Spray polyurethane foam is manufactured on site, from two liquids mixed at the gun. That single fact explains why the installation standard is part of the product standard, and why who sprays it matters as much as which product it is.
The number that causes the most confusion is R-value per inch, because the figure quoted in marketing is an initial reading rather than the aged design value — the thickness question is worked through separately for the vapour barrier case.
Closed-Cell and Open-Cell, Side by Side.
These are the requirements the two Canadian standards actually set. Where a real product's published value is quoted below, it is from a CCMC evaluation or the manufacturer's own Canadian technical data — not from anything we have measured.
- Density: closed-cell at 28 kg/m³ or more; open-cell at 6.8 to 12 kg/m³. That is roughly a threefold to fivefold difference in material.
- Thermal: closed-cell must reach a long-term thermal resistance of RSI 1.80 (R-10.2) at 50 mm, tested to CAN/ULC-S770; open-cell must reach RSI 1.20 at 50 mm, about R-3.4 per inch, with no aging test at all.
- Real Canadian design values at 50 mm cluster from RSI 1.82 to RSI 2.06 — R-10.3 to R-11.7 at two inches, which is R-5.2 to R-5.9 per inch aged.
- Air permeance: closed-cell must be 0.020 L/(s·m²) or lower as a material property, and real products test around 0.002 at 25 mm. Open-cell is only declared at 100 mm, and one common product reaches the air barrier threshold at 89 mm.
- Vapour permeance: closed-cell must be 60 ng/(Pa·s·m²) or lower at 50 mm; open-cell standards set permeance floors instead, deliberately keeping it vapour-open. Published open-cell values run 362 to 1 238 ng/(Pa·s·m²).
- Water absorption: closed-cell capped at 4.0 percent by volume, with real products at 0.5 to 3.3 percent. Open-cell product data states it is not intended for contact with liquid water or below-grade use.
- Service temperature: closed-cell from -60 to +80 °C; open-cell from -60 to +70 °C. Manufacturers require 75 mm of clearance from any device whose surface exceeds 80 °C.
- Blowing agent: since 1 January 2021 it has been prohibited in Canada to manufacture or import a foam product using an HFC foaming agent with a global warming potential above 150, under SOR/2016-137. The Canadian closed-cell market is effectively all HFO now.
Made on Site, in Four Stages.
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Two components, mixed at the gun
An A-side isocyanate and a B-side resin blend meet at a 1 to 1 ratio by volume, under controlled temperature and pressure. Holding that ratio is the whole quality question — foam sprayed off-ratio never fully cures.
- 02
Applied in limited lifts
CAN/ULC-S705.2's baseline is 50 mm maximum per pass, with cooling between passes, because the reaction is strongly exothermic. Published CCMC testing recorded peak in-foam temperatures of 176.5 to 178.5 °C at 125 to 127 mm.
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Cured, then ventilated
Time to re-occupancy is set by CAN/ULC-S774 emissions testing and published in each product's CCMC report. Essentially every current Canadian closed-cell product lists 25 hours, with mechanical ventilation of at least 0.3 air changes per hour during and after installation.
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Covered where the code requires it
Spray foam is combustible. Article 9.10.17.10 requires foamed plastic in a wall or ceiling assembly to be protected from adjacent space, with a carve-out for genuinely concealed attic, roof, crawl space, wall and ceiling spaces.
Frequently Asked Questions About What Is Spray Foam?
Is spray foam R-7 per inch?
Not in Canada. R-7 per inch is an initial figure measured to ASTM C518 on fresh foam. Canadian design values are long-term thermal resistance, and CAN/ULC-S705.1 states that the measured LTTR values shall be the design thermal resistance values, tested to CAN/ULC-S770. Published Canadian 50 mm design values run from RSI 1.82 to RSI 2.06, which is R-10.3 to R-11.7 at two inches, or roughly R-5.2 to R-5.9 per inch aged. Anyone quoting R-7 per inch on a Canadian job is quoting the wrong test.Does thicker foam have a higher R-value per inch?
Counter-intuitively, yes, and it is published. Thicker sections age more slowly at the core, so the long-term value per unit thickness rises with depth. One manufacturer's CCMC-derived ladder gives R-5.3 at 25 mm, R-11.1 at 50 mm, R-17.5 at 76 mm, R-24.1 at 102 mm and R-37.2 at 152 mm — the total climbing faster than a straight multiple of the first inch. Another product shows the same pattern from RSI 1.87 at 50 mm to RSI 4.84 at 125 mm. It is a real material effect rather than a marketing rounding.Closed-cell or open-cell — which should I use?
They are not really competitors. Closed-cell is the material for below-grade walls, rim joists, unvented roof decks, steel buildings, anywhere water or vapour control matters, and anywhere R-value per inch of depth is constrained. Open-cell is vapour-open by design, costs less per board foot, and suits interior partitions and some vented assemblies where a separate vapour control layer is provided. Open-cell cannot be a vapour barrier at any buildable thickness and should not be used in contact with bulk water or below grade — those are not preferences, they are in the standards and the product data sheets.Does spray foam off-gas?
There are three honest answers to three different questions. Properly cured foam does not keep off-gassing — time to re-occupancy is determined by CAN/ULC-S774 chamber testing and comes out at 25 hours for essentially every current Canadian closed-cell product, with the retrofit case conditioned on the area being segregated and ventilated during and after spraying. Foam sprayed off-ratio can produce a persistent amine odour that does not decay, and the only reliable fix is removal; an independent indoor air quality investigator puts the base rate at fewer than one job in two hundred. And the flame retardant TCPP is not chemically bound into the polymer and has been measured emitting more than two years after installation, at indoor concentrations comparable to ubiquitous background sources — the strongest exposures being occupational rather than to occupants.Is spray foam a fire hazard?
It is combustible, which is why the code requires it to be separated from occupied space. As Construction Canada puts it, as a general rule if you can see foamed plastic insulation in the conditioned space of a building, it is a code violation. The documented fire pattern is during application rather than in service: the reaction is strongly exothermic, and over-thick lifts have caused auto-ignition hours after spraying, including three house fires in Massachusetts, one fatal, and a Quebec net-zero demonstration house that burned down in May 2010 hours after attic foam was applied. That is an installer discipline issue — lift thickness, cooling time, and the daily records CAN/ULC-S705.2 requires.Is spray foam always the best insulation?
No. On an open attic floor with room to build depth, blown insulation buys more R-value per dollar and is easier to reverse later. On embodied carbon, even HFO-blown foam carries more than cellulose and generally more than mineral wool or fibreglass per unit of R. Foam's honest niches are air sealing, rim joists, below-grade walls, crawl spaces, complex and unvented assemblies, and steel or post-frame buildings where there is no cavity to fill. Where R-value per dollar is the only question, foam loses, and it is better to hear that from the person quoting it.