Original window trade vintage catalog for SEALED INSULATING GLASS MANUFACTURERS ASSOCIATION. Main office was located at 111 East Wacker Drive, Chicago, IL. Manufacturers of Insulating Glass. Sigma members market factory fabricated hermetically sealed Insulating Glass Units composed of two or more lights of glass separated by an air space containing dry air. Topics discussed are double glazed units, wind load capacity, heating & air conditioning glass properties, percent of window area receiving noon solar radiation, and condensation predictions charts are shown. Unbound from a large 1982 architectural catalog, this unique old four page technical brochure would display wonderful matted and framed. Nice cover graphics. A fabulous addition to your retro windows library. Pages are detached and may contain a small amount of residual glue on edge.