I am, I bought a few packages of it to make armor.
You can buy a can of foam and spray it into a gap; it conforms to the shape of the gap and hardens when it driesYou're probably looking at old hardened spray foam.
probably some cheapo insulation; send the LL a photo if possible
here in Europe its called expanding foam .was put on the heater when new .too much heat loss without it
My tin-foil hat is all ready! Maybe I'll add a propeller so I look extra festive.
