I started with aspen and other kinds of wood mulch, but had a major mite problem and had problems with snakes getting bedding in their mouths when feeding, plus the cost of all that bedding was crazy. I've since switched to paper towels, I really like it and will probably always use it. I just picked up a dwarf reticulated python and boy does she pee! I actually have her on several layers of newspaper. In fact I'm slowly changing over to using several layers of newspaper on the bottom with a top layer or two of paper towels, it's working good for my smaller snakes but the big ones just push aside the paper towels so I have them on newspaper only. I can spray it down with water and the newspaper helps to absorb the extra water and keep the humidity up. Plus it's free! I use wadded up balls of paper towels in the front of each tub and put 3/4 cup water on them every day or two for humidity. So far it's been working great. I can't imagine paying for any other substrate on a regular basis with a whole rack system, just is way too expensive for me. The more free newspaper you can use the better IMO.