1 - 8.5-oz two-part FST Foam Sealant caulking tube; 1 - mixing nozzle; 1 - resealing cap. Protects Conduit and Raceway SystemsFSTâ¢ closed-cell sealant provides superior pressure-blocking in the toughest environments. It stops water, methane, and other gases to keep electrical systems intact. FST Duct Sealant is durable and easy to install. FST is chemically resistant and has excellent adhesion to conduits.