FIREFOAM B2 GUN GRADE 750ML - B2FIREGUN Firefoam B2 Gungrade is a quick setting fire rated, one part polyurethane foam designed for application by any standard foam applicator gun. Fire resistant for up to 2 hours in certain joint configurations. It expands on application to up to 50 times the can contents and meets the requirements of the test criteria for BS476 part 20 and DIN 4102 Part 1 for Construction Materials; Class B2.