I used to use wood chip substrate, then I got tired of picking the dang chips up from what seemed like everywhere.

I switched to paper towels and I couldn't be happier. SO MUCH easier to clean.

When I switched though, the paper towels are obviously much thinner and the snake closer to the actual heating pad, so I got a Rheostat (monitors and keeps temps at a certain level) and it's worked out so much better.