Fibrous glass insulated flexible ducts consist of a spiral wire reinforced inner air barrier core wrapped with resilient fibrous glass insulation and jacketed with an exterior vapor retarder of reinforced foil or plastic film. The light density fibrous glass insulation provides both thermal efficiency and effective noise control. Insulated flexible ducts are available in sizes encompassing most residential and commercial system requirements. (NAIMA members do not manufacture flexible ducts, but do supply the flexible duct industry with fibrous glass insulation.)