Perlite is an that has a relatively high content, typically formed by hydration. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an and a commercial product useful for its light weight after processing.

Due to its low density and relatively low price, many commercial applications for perlite have developed. In the and manufacturing fields, it is used in lightweight and ceiling tiles and filter aids. In it makes composts more open to air, while still having good water-retention properties; it makes a good medium for . Perlite is also used in , insulations, as a lightweight aggregate in and in as a additive.