The term "mineral wool" typically refers to two types of insulation material:

 

Rock wool – a man-made material consisting of natural minerals like basalt or diabase.

Slag wool – a man-made material from blast furnace slag (the scum that forms on the surface of molten metal).

 

Mineral wool contains an average of 75% post-industrial recycled content. It doesn't require additional chemicals to make it fire resistant, and it can be used in two different insulation forms: blanket (batts and rolls) and loose-fill.

 

A Canadian company produces a softer, batt-type mineral product. This product is denser, fits standard wall cavities tighter, and is somewhat less prone to air convection thermal losses than standard fiberglass batt products. Its thermal resistance is approximately R-3.7 per inch, which is comparable with sprayed cellulose insulation or high-density fiberglass batts.