Mineral wool batts are sheets, pads, or bags of low- to high-density fibers made from metal oxides, ceramics, or synthetic minerals. Its appearance is similar to fiberglass or glass wool insulation. Dust and fibers released during handling can cause temporary mechanical irritation to the skin, eyes, or upper respiratory tract. It has a fairly high resistance to flames, but must be kept dry to remain effective and to avoid mold.

The mineral fibers hold together as flexible insulation units. Their batt form differs from rigid mineral-wool boards and from loose mineral fibers placed without an integrated covering.

The fibrous material limits heat transfer within the building envelope. Moisture conditions and the complete assembly affect its performance, separately from the identity of the mineral fibers.