Owens Corning Mineral Wool Safing insulation provides excellent thermal properties in all commercial curtianwall systems. It is made of inorganic fibers derived from basalt, a volcanic rock. The fibers are bonded and formed into flexible batts and will not mildew or support corrosion. It is also fire resistant. Mineral Wool Safing delivers R-values of 4.0 per inch. It cuts easily with a utility knife and is easy to compress to tightly fit between curtainwall insulation and the floor slab.