Owens Corning Thermafiber CI-C SC18 Mineral Wool Insulation Board is the thermal control layer. It is specifically designed for use in the StoTherm ci Mineral system and is available in 2”, 3” and 4” (51mm, 76mm and 102mm) thicknesses. It achieves an R-4.0 per inch (1 PSI – 0.704 m²K/W).