I've used sand, sandy dirt , ash and floor dry. You don't want any thing that can burn, you need it for insulation. That's only a thin gauge . Kitty litter and floor dry are about the same. Each hunting trip, the company supplied half a 5 gal pail of floor dry. More than enough. I just mentioned kitty litter because it's so quick and easy. Use fresh BTW. You dump it out when packing up. I think ash promotes corrosion ?