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Great Stuff, the spray foam insulation, is an effective insulator. Its claim that you can sand it off, though, should be caveated. You can sand most of it off, but the bit closest to the surface is pretty hard to remove, leaving you with a dark yellow stain. The options you have are to either sand down the surface, along with the paint, if there is any, then paint it or to paint over it. So, if you’re sealing up a spot that’s easily visible, it’s probably better to use some kind of clear putty.