GLT Enviro offers flex duct and poly duct. Our flex duct is of high quality and reasonably priced. The flexible tubing which can be used in both medium and low air pressure applications is available in four different sizes and diameters. GLT Enviro poly duct is a clear 4 mil. sheet that is generally used to duct out containment areas. GLT Enviro poly duct is weather and wrinkle resistant and is available in two sizes.