Danish quality perlite for Defender filter or open vacuum filter

Perlite.

Perlite is not a trade name, but the name of a naturally occurring volcanic rock.
It expands when heated in an oven at over 1000°C up to 20 times its original volume. The expansion takes place without additives. The expanded grain is also called perlite. It is composed of countless thin bubbles separated by very thin glass-like cell walls. A new product is formed, white and sterile. This expanded material is then ground into filter perlite using a special technique.