Perlite is a unique volcanic mineral which expands to about 13 times its original volume when it is heated to a temperature of approximately 1600 F (871C). During the heating process, the mineral particles pop like popcorn and form a granular, snow-white material that is so light in weight it weighs only about 5 to 8 pounds per cubic foot (80-128 kg/cubic meter).

Each particle of perlite is comprised of tiny closed air cells or bubbles. The surface of each particle is covered with tiny cavities which provide an extremely large surface area. These surface cavities trap moisture and make it available to plant roots. In addition, because of the physical shape of each particle or perlite, air passages are formed in the growing media thereby providing excellent aeration. Fertilizer appropriate to the plants being grown should be added. Horticultural perlite is available in several different grades. The coarse sand size has been used for many general gardening and horticultural applications, but the finer grades work best when used outdoors.