25 lb. bag, equivalent to 50 lbs. of D.E. Perlite is a lightweight filter media suitable for use in all diatomaceous earth (D.E.) filters. It is an easy to handle, environmentally friendly, all natural, non-toxic product. It removes particles down to 4.0 microns and improves oil absorption. Perlite originates from naturally occuring volcanic rock containing water. When heated, the perlite "pop" and expand 20 times its original volume. This creates a low density and high pore space, ideal for absorption. CelaPerl is used in the same application as diatomaceous earth. Simply precoat your filters with the same number of scoops you use today.