Everbuild firefoam gungrade aerosol everbuild b1firegun firefoam b1 gun grade is a quick setting fire rated one part polyurethane foam it expands on application to yield up to 50 times the can contents and meets the extremely stringent requirements of the text criteria din 4102 part 1 for construction materials class b1 and bs 476 part 20 fire rated up to 4 hours in certain joint configurations for use with an everbuild professional foam gun once cured the foam can be cut sawn or plast