Perlite is not a brand name but a generic term for a naturally siliceous rock. Perlite is distinguishable from other volcanic glasses that, when heat it to a suitable point, expands from four to twenty times its original volume.

This expansion is due to the presence of combined water in the crude perlite rock. When quickly heated to above 1600 degrees F (900 degrees C), the crude rock expands in a manner similar to popcorn as the combined water vaporizes and creates countless tiny bubbles that account for the amazing light weight and other exceptional physical properties of expanded perlite. The expanded perlite's most distinguishing characteristic is its white color. While the crude rock may range from transparent light gray to glossy black, the color or expanded perlite ranges from snowy white to grayish white.

Expanded perlite can be manufactured to weigh to as light as 2 pounds per cubic foot (32 kg/m3) making it adaptable for numerous applications. Since perlite is a form of natural glass, it is classified as chemically inert and has a pH of approximately 7.