Newspaper, reptibark, aspen and now paper towels. Seven tanks. My wife likes natural, but reptibark and even aspen don't always spot clean well. And I don't want to argue, just stick your head in there and take a good sniff ( I dare you). Reptibark holds moisture well, looks great. Paper towels are my favorite though. Hope that helps, we were using aspen. Spot cleaning very thorough, still stunk. Might as well get the benefits of the reptibark, if your going for looks. Peace, don't go nuts we have this debate to often.