Tested and catalogued according to UL 181 / ULC S-110, class 1 air ducts. A one ply aluminum foil closely corrugated for strength and flexibility with seems QUADRALOCKED®, folded flat and knurled to insure air tightness. 

TYPE S duct will be of semi-rigid construction capable of maintaining the shaping required by job conditions without subsequent sagging or droop. Duct connections to equipment outlet collars shall be made in accordance with the duct manufacturer's recommendations.