Mineral wool is a fibrous insulation material manufactured from molten rock, slag, or glass spun into fine fibers and bound with organic binders. It provides R-values between R-3 and R-3.5 per inch while offering superior fire resistance, achieving non-combustible ratings required by building codes. Mineral wool resists moisture absorption better than cellulose while remaining breathable for vapor management.
Types and Fire Performance
Rock wool (basalt fiber) and slag wool deliver consistent thermal performance with melting points exceeding 1200°F. Unlike fiberglass at R-3.2 to R-3.8 per inch, mineral wool achieves fire ratings without additional treatments, making it ideal for party walls, fire-rated assemblies, and commercial applications requiring ASTM E84 compliance. Density typically ranges from 0.75 to 2.0 pounds per cubic foot.
Building Applications
Mineral wool batts, blankets, and loose-fill formats accommodate various cavity dimensions. Its fibrous structure provides acoustic damping alongside thermal insulation, reducing sound transmission class (STC) ratings in wall and floor assemblies. Mineral wool’s hydrophobic properties and fire resistance make it preferred for exterior continuous insulation, mechanical spaces, and areas requiring enhanced safety without sacrificing thermal performance.