Perlite is a generic term for naturally occurring silicous rock. The distinguishing feature which sets perlite apart from other volcanic glasses is that when heated to a suitable point in its softening range, it expands from four to twenty times its original volume.

Therefore it can take up loads of water and in contrast to vermiculite dispens hunidity to its environment.

It´s the perfect material for high hunidity in growing chambers, but not useable for substrate production!

Coronation: < 5 mm
Water absorption: 50 % of volume