[Arran]

Ah yes, the Philco "Green Death" strikes again, someone suspected that cellulose nitrate based insulation might be to blame, which is what they used to make movie film out of, the explosively flammable kind. I have thought that a strip of acetate based photographic film would work, but there are so many types of sheet plastic around that you could just about use anything, PETE, Kapton tape, polypropylene.
Since it is a battery radio it is possible that the set wasn't stored in a climate controlled setting, like a barn, or attic, for many years, but that's conjecture on my part.
Regards
Arran