ThermoFlo Technologies 'SRB' series is an industrial quality insualted duct manufactured "tough" for consumers' and installers' peace of mind. It 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 insulation reduces heat loss & condensation.