GREAT STUFF Fireblock Insulating Foam Sealant is a ready-to-use, minimal-expansion insulating foam sealant that fills and insulates gaps up to 3/4 inch to restrict airflow. This distinctly orange solution seals electrical wiring run through wall studs as well as service penetrations in walls and between floors to provide a simple, cost-effective way to maintain the continuity of an approved fire block material throughout the house.