GREAT STUFF PRO™ Gaps & Cracks Insulating Foam Sealant is a minimal expanding, single component polyurethane foam sealant for professionals or larger projects like general purpose building envelope air sealing. In the United States, the sealant is easily identified by its bright color. It has led the way in the industry by being recognized as a fireblock, which means it resists the free passage of flames to other areas of the building through concealed spaces.