Abstract: An air conditioning or heating duct system for insulation in raised floor or dropped ceiling environments includes a strip of flexible material, such as foam rubber or the like, having a width approximately equal to the distance between a sub floor and a raised floor or between a main ceiling and a drop ceiling and having a length determined by the path that the cooled or heated air must follow throughout the raised floor or dropped ceiling area. The flexible strips are fastened by U-shaped brackets where the conditioned air enters or leaves the space which is to be heated or cooled, with additional brackets positioned at points where bends in the flexible materials are made. A system according to the present invention may either include double-spaced apart strips of flexible material to form air ducts or it may include a single strip of flexible material to direct or deflect the cooled or heated air into a first portion of a space to be controlled and not into a second portion of a space to be controlled.