^^ agree ^^ All foams have sizable flame spread ratings, it also gives off acrid smoke when burning. It IS a chemical.
So, it HAS to be covered with sheetrock to achieve a safe fire rating.
Now there's also Rockwool, "safe and sound" batt insulation. Its made from mineral wool and wont burn. But its expensive, about $1 per square foot of surface area.
SAFE'n'SOUND Sound Proof Insulation | ROCKWOOL
