Perlite is composed of minerals that have been subjected to high heat which caused it to "plump" up and expand.
The end result of this process is a very porous and light weight absorbent mineral foam. Perlite has many construction and industrial applications. It also has multiple horticultural applications. It is is used as a soil amendment and in soilless gardening / hydroponics it is used as a growing media..
Perlite has a neutral pH and will not affect the alkalinity or acidity of your solution.
It is inexpensive and reusable.
It is very porous and has excellent wicking action, meaning that it will absorb and draw up liquids via capillary action. It draws up nutrient solution and water from the reservoir at a steady rate, it avoids excessive waste of water and nutrients.
In many commercial hydroponic crop operations, perlite is usually contained in perforated grow bags. Aerated nutrient solution is maintained in the perlite by placing the bags in a shallow reservoir. Perlite's unusually strong capillary attraction automatically draws up the reservoirs solution at a rate that is equal to that lost by transpiration. Transpiration is the movement of water within plants and the loss of water via evaporation through its foliage.
Perlite has significant disadvantages when not used in conjunction with other media.
1. It is extremely lightweight and buoyant. Its buoyancy causes it to float - hence it does not perform the task of anchoring the plants very well. This disadvantage is most bothersome in flood and drain or ebb & flow systems. In these systems , the perlite floats away and is a general nuisance.
2. It produces dust that is not only unhealthy for humans, but is also a nuisance in the solution as it contributes to sludge and clogging. It must be thoroughly washed before using.