Rock wool

Similar to other glass fibers, the chemical composition of rock wool and slag wool are primarily aluminum and silicon oxides. However, these wools possess a higher alkaline earth oxide content (MgO and CaO) and lower alkali metal oxide content (Na2O and K2O) than glass wool. It is used as for residential, commercial and industrial insulation. Rockwool is very effective for use as insulation behind and around electrical boxes, wires and pipes. It can fill most wall cavities, leaving virtually no voids. It is also used as spray-on fireproofing material.