Perlite is a lightweight granular material that is white in color and is made by heating volcanic glass, heated to 1000°C until it pops, similar to popcorn. It is neutral in pH, i.e., it is neither alkaline nor acidic. Perlite is typically made from the hydration of obsidian, a natural volcanic glass. It is used as a soil additive to improve aeration and modify the soil substructure, keeping it loose, well-draining, and defying compaction.