Perlite is a naturally occurring volcanic glass. When heated rapidly, the water it contains turns to vapor and expands the particles into a lightweight porous material.
In construction, expanded perlite is used as aggregate in lightweight concrete and plaster, as loose-fill insulation, and in specialist fire-protection or acoustic systems. The tested assembly, not the material name alone, defines each application.
A buyer or client should request density, thermal conductivity, fire classification, and the intended use of the exact composition in the project. Those values should then match the working drawings and installed work.