SPRAY FOAM: “What Kind Should I Use?”

Question: Do you have a recommended brand and type of spray foam in a can, other than the usual closed cell polyurethane foam you see in hardware stores everywhere? I’ve got some small DIY jobs and I also want to seal around the perimeter of some windows I’ll be installing.

Answer: For regular sealing jobs (i.e. non-window and non-door installations), the common type of closed cell polyurethane foam in small cans works very well. I’ve used other formulations in cans and none are as good as polyurethane. I’ve also never noticed any difference between one brand of polyurethane spray foam and another.

The nice thing about polyurethane spray foam (besides being widely available) is that if it’s applied thick enough, it acts as its own vapour barrier, preventing internal condensation when the weather gets cold. How thick is thick enough? Two inches is considered a minimum, and 3″ thicknesses is even better.

Now, if you’d want to seal around windows and doors, definitely do not use ordinary polyurethane foam. It expands too much and will often cause door and window frames to bow inwards, preventing them from opening and closing properly. Even so-called “low-expansion” foam in a can often expands too much for use around doors and windows. I learned the hard way that foam made especially for doors and windows is the only stuff worth using. Look for that wording on the label, along with the words “low pressure”.

Even then I always install temporary wooden props on the inside edges of frames, to support them and resist the inward bowing caused by foam expansion, just in case.  I usually use any kind of scrap like 2x2s cut to just the right length to provide support to the window jambs when the 2×2 is slipped in between the two horizontal jambs. Leave these props in place for a week if possible before removing them. Foam can continue to expand slightly even after it appears fully cured.

Do you have a larger surface you want to spray with foam, but smaller than you can justify having a spray foam contractor come out and do the work? DAP has come out with a single-part spray foam system that’s made to cover intermediate situations. You can see it in action on one of my projects below.

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