Open-Cell vs Closed-Cell Spray Foam: Which One Does Your Project Need?

If you're comparing spray foam quotes and one is dramatically cheaper than the other, the first question isn't "who's the better deal" — it's "are they even quoting the same foam?" Open-cell and closed-cell spray foam are two different products that happen to be installed with similar equipment. Mixing them up is the most common — and most expensive — mistake homeowners make.

Closed-cell foam (2 lb density) is the dense one. It sprays hard, gives you roughly R-6 to R-6.5 per inch, and — critically — acts as a moisture vapor barrier. That matters in Canada, where warm indoor air hits cold sheathing for half the year and condenses. Closed-cell stops that condensation dead. It also adds structural rigidity to walls and roofs, which is why builders love it for metal buildings and pole barns.

Open-cell foam (0.5 lb density) is soft and spongy. It gives about R-3.6 to R-4 per inch, so you need more thickness to hit the same R-value. It does not stop moisture vapor — it's vapor-permeable — so it is the wrong product anywhere a vapor barrier is required (basements, crawlspaces, cold climates in general). What open-cell is genuinely good at is sound dampening and filling large, odd-shaped cavities cheaply, like an open attic floor where you don't need a vapor barrier.

The rule of thumb for Canadian projects: closed-cell for anything that touches a cold surface or needs moisture control — exterior walls, basements, crawlspaces, rim joists, cold storage, vehicles, and metal buildings. Open-cell only for interior soundproofing or an open, ventilated attic floor where you're insulating for heat, not moisture.

A contractor who quotes "spray foam" without naming the type is either being vague on purpose or doesn't know the difference. Both are red flags. The quote should say which foam, at what thickness, and the resulting R-value. If it doesn't, you're not comparing quotes — you're comparing guesses.