Fibrous glass duct insulation means enhanced comfort. It helps to ensure that heated or cooled air will be transmitted from central air equipment to working and living spaces at comfort levels suited to occupants' needs. Increased occupant comfort in commercial buildings contributes to increased productivity; in residential buildings, to an enhanced sense of well-being. In either case, fibrous glass duct insulation allows the building owner to utilize central equipment effectively-or, in many instances, to provide desired comfort levels with central equipment of less capacity and cost than would be required when ducts are not thermally insulated.