Evaluated Alternative Natural and recyclable insulation material ROCKWOOL stone wool insulation is made from volcanic rock. Stone wool is naturally non-combustible (containing no harmful chemical flame retardants) and will not give off any significant amount of toxic smoke during a fire. Additionally, stone wool lasts more than 60 years without any loss of thermal efficiency, non-combustibility or dimensional stability. It can also be endlessly recycled at a growing number of locations, helping to reduce the amount of construction waste going to landfill.