12" x 25' - Flexible Aluminum Duct Hose Hart & Cooley 044790 12" x 25' Non-Insulated Flexible Air Duct Connector 12" diameter x 25' length; Double-ply metalized polyester core; Class 1 air connector Rated pressure per UL 181: 16" W.C. positive, 1/2" W.C. negative Recommended maximum operating pressure: 6" W.C. positive; rated maximum air velocity: 6000 fpm UL-Listed (UL 181)