Perlite is a volcanic material heated to 1,800 degrees making it porous. The particles provide excellent drainage while trapping air and water on its' irregular surface. Perlite will hold 3-4 times it own weight in water. It is neutral in reaction and has no buffering action.
It is normally used in a 50/50 mix in hydroponics, sometimes adding coco peat for extra water holding ability. It can be mixed with soil to allow for better aeration of the medium. Sold 6 cubic foot bales.