Expanded perlite based on naturally occurring silicate rock

The distinguishing feature of perlite from other volcanic glasses is that when it is heated to a suitable point in its softening range, it expands from four to twenty times its original volume. This expansion is due to the presence of two to six percent of combined water in the crude perlite rock. Its unique internal structure consists of numerous tiny closed air cells surrounded by a large exterior irregular surface. When quickly heated to above 160degF (871degC), the crude rock pops up in a manner similar to popcorn as the combined water vaporizes and creates countless tiny bubbles which account for the amazing light weight and other exceptional physical properties of expanded perlite.