Open-Cell vs Closed-Cell Spray Foam: What Calgary Homeowners Should Actually Compare

If you’ve been handed a spray foam quote, two words on it decide almost everything about how the job performs: open-cell or closed-cell. They are not two grades of the same product. They behave differently, they cost differently, and only one of them can do double duty as your vapour barrier.

Here’s how to tell which one your house needs — and how to read the R-value on that quote, because the number most people quote is not the number Canada publishes.

The short version

Closed-cell is the dense one. Its cells are sealed shut, which is what lets it block air and moisture and cure hard enough that you can knock on it.

Open-cell is the light one. Its cells are open, so it stays soft and spongy. It still stops air movement, but water vapour passes straight through it.

	Closed-cell (medium density)	Open-cell (light density)
Feel when cured	Rigid, hard to the touch	Soft, spongy
R-value per inch (Canadian design value)	R-5.1	R-3.6
Air barrier	Yes	Yes
Vapour barrier	Yes, at the right thickness	No, never
Expands	Roughly 30 to 40 times	Much more, fills large voids
Adds structural rigidity	Yes	No
Relative cost per inch	Higher	Lower
Typical Calgary uses	Rim joists, crawl spaces, cantilevers, cathedral ceilings, foundations	Interior walls and sound control where a vapour barrier already exists

That vapour barrier row is the one that matters most in our climate, and we’ll come back to it.

The R-value number on your quote is probably too high

This is the single most useful thing a Calgary homeowner can learn about spray foam.

You will see closed-cell foam advertised at R-6, R-6.5, sometimes R-7 per inch. Freshly sprayed, that is roughly true. But closed-cell foam is blown with gases that slowly escape and are replaced by air, and as that happens the insulating value drops and settles at a lower long-term number.

Natural Resources Canada handles this directly. In its Keeping The Heat In materials table, NRCan notes that freshly applied closed-cell foam starts around RSI 1.06 per inch, but that “due to the loss of the foam’s blowing gases over the immediate and long term, its RSI value should be limited to only 0.90.”

Converted to the R-values homeowners actually use:

	Fresh	NRCan design value
Closed-cell spray foam, per inch	R-6.0	R-5.1

That’s about 15% lower than the fresh number. Over the life of your house, R-5.1 per inch is the honest figure to budget around. A contractor quoting R-6.5 per inch isn’t necessarily lying — they’re quoting day-one performance rather than the aged value the country’s own energy authority publishes.

Ask which number your quote is based on. A good answer is a specific one.

Open-cell’s R-value surprises people

Here’s the comparison against everything else on the market, using NRCan’s published design values per inch of thickness:

Material	RSI per 25.4 mm	R per inch
Closed-cell spray polyurethane foam	0.90	R-5.1
Open-cell spray polyurethane foam	0.63	R-3.6
Cellulose, blown, settled	0.63	R-3.6
Glass fibre batt	0.56	R-3.2
Glass fibre, loose fill, blown	0.51	R-2.9

Read that table twice. Open-cell spray foam and blown cellulose have identical R-values per inch. Open-cell is only about a quarter better per inch than a fibreglass batt.

So if somebody is selling you open-cell foam on the strength of its R-value, the pitch doesn’t hold up. Open-cell earns its place a different way: it stops air movement, it expands enormously so it fills irregular cavities completely, and it’s softer on the budget than closed-cell. Those are real benefits. Raw thermal performance per inch is not one of them.

If R-value itself is new to you, our guide to R-values for Calgary homes covers what to target in each part of the house.

Air barrier, vapour barrier: the distinction that matters in Calgary

These two terms get used interchangeably in sales conversations. They are not the same thing, and in a Calgary winter the difference shows up as moisture in your building assembly.

An air barrier stops air from moving through the assembly. Both foams do this. According to CUFCA, the Canadian Urethane Foam Contractors Association, all medium-density spray polyurethane foam “is an air barrier material at the minimum installed thickness allowed of 12mm” — that’s under half an inch.

A vapour barrier stops water vapour from diffusing through. This is where the two products separate completely.

Closed-cell foam can serve as the vapour barrier, but only once it’s thick enough. The Canadian material standard, CAN/ULC-S705.1, sets a maximum water vapour permeance of 60 ng/Pa·s·m² measured on a 50 mm specimen — 50 mm being just under 2 inches. NRCan agrees, noting that closed-cell foam “when applied to a thickness of 50 mm (2 in.), it can sometimes act as a vapour barrier.”

Open-cell foam does not get there at any thickness. NRCan is blunt: it “can be used as an air barrier but not a vapour barrier.”

This is exactly why our spray foam installations specify a minimum 2-inch layer of 2 lb foam on an attic floor. It isn’t an upsell — it’s the thickness at which the product starts doing the second job you’re paying it to do. Below that, you have air sealing and insulation, but you still need a separate vapour control layer.

If you take one thing from this article: in Calgary, if the plan is for the foam to be your vapour barrier, it has to be closed-cell and it has to be at least 2 inches.

What “2 pound foam” actually means

You’ll hear closed-cell called “2 lb foam” and open-cell called “half pound foam.” Those are nicknames for density.

The Canadian standard is more precise. CAN/ULC-S705.1 sets a minimum apparent core density of 28 kg/m³ for medium-density closed-cell foam — which works out to about 1.75 lb/ft³. So “2 pound foam” is a rounded-up nickname for a product with a published minimum floor beneath it.

Density is worth understanding because it drives everything else in the table above: the denser product is the one that resists vapour, adds rigidity, and delivers more R per inch.

Where each one belongs in a Calgary house

Closed-cell makes sense where you need moisture control, strength, or performance in a shallow space:

• Rim joists and the band around the top of your basement wall
• Crawl spaces
• Cantilevers and bonus rooms over a garage, where the cavity is fixed and every inch has to work hard
• Cathedral and vaulted ceilings with no room for deep insulation
• Foundation walls and below-grade applications
• Problem areas where air is clearly leaking and nothing else has worked

Open-cell makes sense where the vapour control is already handled:

• Interior partition walls, largely for sound
• Cavities where a vapour barrier is already in place and intact
• Situations where you need a foam to expand into an awkward, irregular void

And there’s a third answer that often beats both: for a big open attic floor, blown fibreglass insulation usually gets you to the same target for a fraction of the cost, because in an attic you have unlimited depth to work with. Depth is cheap up there. Foam’s advantage is performance per inch, and that advantage is worth paying for only where inches are scarce.

We see the same pattern in finished spaces, where batt insulation in a standard stud bay is the sensible product and foam is reserved for the details around it.

Questions to ask before you sign a spray foam quote

Spray foam is installed by a crew, on site, in one pass. Unlike a batt you can inspect on a shelf, the quality of the finished product depends almost entirely on how it was mixed, sprayed and cured that day. So the questions worth asking are about process.

1. Open-cell or closed-cell, and why this one for my house? A good contractor will tie the answer to vapour control, not just to R-value.
2. What thickness, and what R-value are you basing that on? Fresh or aged.
3. Is the installer CUFCA certified? CUFCA’s Quality Assurance Program requires a licensed contractor to have “at least one certified installer on each job site at all time,” with certification renewed annually.
4. Will I get the daily work record? The program requires “detailed daily work sheets providing a paper trail of testing results, site conditions, installers etc.” Ask for your copy.
5. Which standards does the material and installation meet? The answers should be CAN/ULC-S705.1 for the material and CAN/ULC-S705.2 for the installation.
6. How long do we need to be out of the house? Plan on vacating for 24 hours after application.

A contractor who answers those six cleanly is a contractor who has done this properly before. If you’d like ours answered for your house, get in touch and we’ll walk through them on site.

And if you’ve run into other confident claims about insulation that didn’t sit right, we’ve collected a few in insulation myths debunked.

FAQ

What is the difference between open-cell and closed-cell spray foam? Closed-cell foam has sealed cells, cures rigid, blocks both air and vapour, and delivers about R-5.1 per inch as a design value. Open-cell foam has open cells, stays soft, blocks air but not vapour, and delivers about R-3.6 per inch.

What is the real R-value of closed-cell spray foam per inch? Natural Resources Canada publishes a design value of RSI 0.90 per 25.4 mm, which is about R-5.1 per inch. Fresh foam tests higher — around R-6 — but the value drops as the blowing gases escape, so the lower number is the one to plan around.

Is spray foam a vapour barrier? Closed-cell foam can be, at roughly 2 inches (50 mm) or more. The Canadian material standard CAN/ULC-S705.1 caps water vapour permeance at 60 ng/Pa·s·m² on a 50 mm specimen. Open-cell foam is never a vapour barrier at any thickness.

How thick does spray foam need to be to act as an air barrier? Much thinner than people expect. CUFCA states that medium-density spray foam is an air barrier material at the minimum installed thickness of 12 mm, under half an inch. Air sealing and vapour control are two different jobs with two different thresholds.

What does “2 pound” spray foam mean? It’s a nickname for density. CAN/ULC-S705.1 requires a minimum apparent core density of 28 kg/m³ for medium-density closed-cell foam, roughly 1.75 lb/ft³.

Is open-cell spray foam worth it? It can be, for sound control and for filling awkward cavities where vapour control is already handled. Just don’t buy it for R-value — per inch it performs the same as blown cellulose and only slightly better than a fibreglass batt.

How long do I have to stay out of the house after spray foam? Plan on 24 hours after application before re-occupying.

Do I still need a poly vapour barrier if I use closed-cell foam? If the closed-cell foam is thick enough to meet the permeance requirement, it can serve that role itself. That call belongs to whoever is designing the assembly, and it should be settled before the crew arrives, not after.vs Cloccd-Cell Spray Foam: What Calgary Homeowners Should Actually Compare