Course DE(Diatomaceous earth)also found in big bags at auto parts store label as floor dry/absorbent. Just look at the label to make sure it says natural clay or diatomaceous earth itself. I will be by the local Napa today and will get the actual part number and post it this evening. Anyways DE holds both air and water and many have used it in place of perlite for along time....also works as a soil dwelling pest repellent.....