Only mentioned as windows are biggest heat loss sources other than doors, and this bus has tons of windows obvsly. I'm with you on that point. What's the leas

Only mentioned as windows are biggest heat loss sources other than doors, and this bus has tons of windows obvsly. I'm with you on that point. What's the least flammable insulation available for body filling, fiberglass? Edit: ceramic or rock wool perhaps, but mind the dust and know which treatments were applied.