... ventilated,not corrosive the aluminum pipe 2.package:PE insulated flexible duct is made of aluminum foil + pet +steel wire ... (such as school, supermarket, office, stadium, theater, factory…),high requirement of the environment area, such as hospital, laboratory, ... howff, bus, train, broadcasting studio.Specifications:Structure: High elastic wire, aluminum foilStandard Diameter: 3, 4, 5, 6 ...