Mineral wool is becoming a viable option for continuous, exterior thermal performance in a building system. It was first observed on the Island of Hawaii in the 19th century, when molten volcanic lava was stirred by the wind into fibers that the natives used to blanket their huts. A method of manufacturing this natural mineral fiber was first patented in the United States in 1870 by John Player. Twenty-seven years later, American Engineer Charles Corydon Hall developed a technology to transform molten limestone into fibers and launched the rock wool insulation industry in America.
Today’s mineral wool insulation is produced by heating a molten mix of basalt, or dolomite and slag, derived from steel manufacturing in a furnace at a temperature of about 1,426 degrees Celsius (2,600 degrees Fahrenheit), through which a stream of air is blown. More advanced production techniques involve whirling molten rock and a polymer binder using high-speed spinning heads somewhat like the process used to produce cotton candy. The final product is a mass of fine, intertwined fibers with a diameter that ranges from two to six micrometers. It is typically comprised of mostly inorganic material.