The following two major Divisions comprise Insulfoam: Insulfoam - Largest US producer of block molded expanded polystyrene. Major supplier to the construction, insulation and OEM markets. Computer aided design, engineering and manufacturing capabilities. Premier Building Systems - North America's largest manufacturer and exporter of Structural Insulated Panels (SIPs) used for commercial and residential building. SIPs are sandwich panels with an expanded polystyrene insulating core between two sheets of engineered wood, resulting in an energy efficient and exceptionally strong building system.