Perlite is a unique volcanic amending soil mineral which expands from four to twenty times its original volume when it is heated. Perlite can reach temperatures of approximately 1600-1700 degrees F. The media's expansion is due to the presence of two to six percent combined water in the crude perlite rock, which causes the perlite to pop in a manner similar to that of popcorn. When expanded, each granular, snow-white particle of perlite is sterile with a neutral pH and contains many tiny, closed cells or bubbles. The surface of each particle is covered with tiny cavities which provide an extremely large surface area. These surfaces hold moisture and nutrients and make them available to plant roots. In addition, because of the physical shape of each particle, air passages are formed, providing optimum aeration and drainage. Because perlite is sterile, it is free of disease, seeds, and insects.