If you are going to put this foam in something else, I wonder if that
expanding "Great Stuff" spray foam would be of help. (home depot,
lowes, etc).

If, for instance, you were thinking of putting your sheet in a hold or
something, you could spray this expandable foam instead.
I don't know if it 'likes' to be wet and turns to a sponge - but that
you could easily test for.

Regards,
Remco