I'm about to begin work with my plumber on my remodel and have a bunch of scrap 1-1/2" and 3" polyiso laying around the site. I've installed 3" on the exterior of the building and need some insulation in the stud cavities. Tomorrow, my plumber will be installing a tub and I'll need to insulate the two stud cavities before we install the tub. As my walls are of the dry-to-the-inside variety, I'm thinking that it's probably not a good idea to cut my scrap foil-faced polyiso and pack it in there? My ultimate plan is to fill the stud cavities with fiberglass when the time comes, but tomorrow, I was thinking I might be able to use some of the polyiso scrap I have.