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Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.
Perlite softens when it reaches temperatures of 850–900 °C (1,560–1,650 °F). Water trapped in the structure of the material vaporises and escapes, and this causes the expansion of the material to 7–16 times its original volume. The expanded material is a brilliant white, due to the reflectivity of the trapped bubbles. Unexpanded (“raw”) perlite has a bulk density around 1100 kg/m3 (1.1 g/cm3), while typical expanded perlite has a bulk density of about 30–150 kg/m3 (0.03–0.150 g/cm3).

Perlite are used to masonry construction, cement, and gypsum plasters and loose-fill insulation.
Perlite is also a useful additive to gardens and hydroponic setups.

They mainly stem from its unique physical and chemical properties:
Perlite is physically stable and retains its shape even when pressed into the soil.
It has a neutral pH level
It contains no toxic chemicals and is made from naturally occurring compounds found in soil
It is incredibly porous and contains pockets of space inside for air
It can retain some amount of water while allowing the rest to drain away
These properties allow perlite to facilitate two critical processes in soil/hydroponics, which are essential for plant growth.