LeAnn, I've heard kitty litter isn't great, but don't remember why. A lot of people use carefresh or it's generic counterpart that you can find at walmart. I've also heard orchid bark or cypress mulch from a garden center. Some people throw it in the freezer first just in case there may be creepy crawlies in it. I think a fair number of people use aspen as well. No pine or cedar, though. Oh, and some use that compressed stuff, either corn or paper/wood product. That may be found in the kitty litter section? Just make sure there are no 'magic crystals' or anything like that... just compressed natural material.