Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. In the construction and manufacturing fields, it is used in lightweight plasters and mortars,insulation and ceiling tiles.In horticulture, perlite can be used as a soil amendment or alone as a medium for hydroponics or for starting cuttings. When used as an amendment it has high permeability / low water retention and helps prevent soil compaction