Perlite is a heat expanded, man made product for use as a hydroponic growing medium. Perlite retains enough moisture for it to be suitable as a hand watered medium, but also has sufficient drainage to be used in a recycling drip irrigation system. Perlite is extremely lightweight and is suitable for use in a variety of growing containers pots, trays, bottom fed auto watering systems, etc.

Vermiculite is another heat expanded product which has very high water retention - often used as a soil conditioner or for covering seed raising mixes. Vermiculite holds too much water however to be useful as a medium by itself, but can be mixed with other growing mediums to improve the water retention and extend the period between waterings.