Add porosity to your soil and soilless mix by using Mother Earth® Perlite. Mother Earth manufactures one of the best perlites on the market. Perlite is a naturally occurring siliceous rock that when heated to 1600 F expands up to 20 times its original volume. Mother Earth utilizes these properties to make the very best perlite through a kilning process. It is very similar to popping popcorn and produces a growing medium that is sterile and has a neutral pH of 7.0. 4 cubic feet per bag.