Conduits and ducts either composed of or lined with fibrous glass insulation media such as batts, mats, boards or the like are commonly used in heating, cooling and ventilating systems. The construction and method of making these conduits is described in U.S. Pat. Nos. 3,092,529; 3,212,529 and 3,394,737. A protective coating or film is generally applied to the inner air directing surfaces of these ducts to insure a smooth, low friction producing surface being presented to air flowing through and being directed by the duct.
The properties commonly required of these coating include a smooth surface when dried or hardened, water or moisture resistance, ability to be applied by dipping, brushing, spraying or the like and low flame spread and smoke characteristics. Flexibility of the coating without cracking or breaking away from the fibrous glass surface after it is hardened is also highly desirable when the coating is applied to flexible ducts.