ThermoFlo Technologies 'SRB' series is an industrial quality insulated duct manufactured "tough" for consumers' and installers' peace of mind. It features the high standard c-ETL-us / Can / ULC-S110-M86 / UL 181 approved cores from ThermoFlo. The 'SRB' series duct consists of a three ply polyester laminate, fiberglass reinforced scrim, galvanized spring steel wire, wrapped with fiberglass insulation, which provides an outstanding combination of strength and tear resistance. A heavy duty fire retardant black polyethylene vapor barrier adds extra durability. The ThermoFlo 'SRB' series ducting is marked approximately every foot and is easy to install. Instructions are included with each case. The insulation reduces heat loss & condensation. This product is certified by the US / Canadian Certification ETL Mark. Made in Canada! North America's best quality product. *Also available in custom order lengths.