I use both paper and aspen. I would choose paper any day, but my Dumeril's boa needs to burrow. Aspen is nice for a week or two, then it starts to get nasty (even with spot cleaning) it works fine of you are using an overhead heat source like a heat lamp, CHE, or RHP. But if you are using a UTH it really can become a pain since it doesn't transfer heat very well.