I've been experimenting a little with expanded clay as an insulating aggregate. The stuff is much denser than perlite or vermiculite, but is also way stronger. I have been using it where I want an insulator, but also need strength in that area. It has replaced a 50/50 mix of heavy aggregate and perlite. Because of the way the stuff is manufactured it is really strong. each grain is around 10 mm in diameter and are spherical in form. The outside is quite hard but the inside is full of holes and much softer.This is ideal because it gives them more strength while remaining pretty light. They cost me around double that of perlite, but I think I'll continue to use them. Anyone else had experience with using them or know of any building applications? They are generally used as a water filtration or water storage as a growing medium.