Mineral Wool
Mineral wool (also called rock wool or stone wool, sold under the Rockwool brand) is an insulation made by spinning molten basalt or slag into fibers. Mineral wool batts and boards are denser than fiberglass, naturally fire-resistant (over 1,000°F melt point), water-shedding rather than absorbing, and acoustically dense. R-value runs about R-3.7 to R-4.3 per inch — slightly higher than fiberglass. Mineral wool is the standard high-performance batt insulation outside North America and is increasingly common in Passive House builds.