This is my first attempt at sealing a window frame with expanding foam (I used the kind for windows and doors).

I cut off the excess with an oscillating saw blade with teeth, and I'm a little alarmed at the appearance - are all these bubbles OK?

Would I be completely silly to cover it up with some self adhesive aluminum flashing (the kind you'd normally see on the outside)?

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  • 3
    Technicality: not air but gas. There's air in there now because the holes are exposed to the air, but inside the foam there will be some sort of gas that's not actually air. (i.e. you can't breathe it for very long.) Oct 25, 2022 at 15:03
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    Without being too picky here, air is a gas.
    – SteveSh
    Oct 25, 2022 at 15:15
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    "Foams are materials formed by trapping pockets of gas in a liquid or solid."
    – Dan Mašek
    Oct 25, 2022 at 17:11
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    @SteveSh Probably being a bit too picky, air is a mixture of different gases.
    – Reznik
    Oct 26, 2022 at 8:43
  • 2
    It's a foam... By definition it contains pockets of gas... Oct 26, 2022 at 14:36

2 Answers 2


Yes, it looks fine. I wouldn't worry about the little voids.

Putting flashing over this would serve no purpose at all, and it might make it harder to install the drywall and window trim.

  • 4
    Yup. This is exactly what the foam looks like when you cut open the smooth skin on the outside.
    – FreeMan
    Oct 25, 2022 at 12:44
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    How big of void would they need to be before you would worry about them?
    – R.M.
    Oct 25, 2022 at 21:42

Pat yourself on the back you did a great job. You will be saving money on both heating and cooling for many years to come.

It is the trapped air in the bubbles that do the insulating so that is a good thing. As I understand it the smooth outside happens because the bubbles break until and surface tension smooths it out. As the surround material sets up it fixes them in place.

You can cover it as you wish with drywall or whatever. The foam is not structurally sound so anchoring something to it is not a good idea. That will not be a problem as you have a lot of supporting structure around it to support drywall or whatever you decided to cover the wall with.

  • Thanks! I usually have a bad time with this foam. :)
    – negacao
    Oct 25, 2022 at 16:09
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    +1 for including the main point: that the air pockets are what's doing the work providing insulation. The foam body material is just to keep them trapped as opposed to having free moving air like you would without it. Oct 26, 2022 at 16:21

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