A Closed-Cell Foam Duct Sealing System for Conduit Sizes up to 2"/50mm. ZipSeal™ Duct Sealant is a practical and efficient way to seal small conduits and communication innerducts. The revolutionary Zip-Disc™ insert traps and keeps the foaming liquid in its open-cell (center) area. Cured foam blocks can be removed and re-entered relatively quickly if necessary.