Perlite is possibly the most commonly used soil amendment for drainage. This porous, and lightweight white material is actually made from 'puffed' volcanic rock, heated to extremely high temperatures, which creates millions of tiny holes in the expanded rock-like material. think of rice krispies, which consist of puffed rice, a very similar concept. HOWEVER- don't eat perlite for breakfast, and don't use the rice krispies for drainage in your soil either!