Flexible Duct Connector? All Duro Dyne Fabrics are designed to meet NFPA 90A & 90B.? All Duro Dyne Fabrics are airtight and waterproof.? All seams are secured with Grip-Loc or Guard Loc, a Metal to fabric heavy duty gripping method.? All Duro Dyne Flexible Duct Connector utilize 24 or 28 gauge (.7 mm or .47 mm) galvanized steel meeting ASTM-A-525 G60.? Flexible Duct Connector is available with 300 series stainless steel or aluminum.? Duro Dyne Flexible Duct Connector is manufactured in the United States.