Reptile bark, currently. I prefer the Aspen and Lava, our first cornsnake, appeared to prefer it also because she was small and it was easier to burrow in that the reptile bark. However, it was very drying to her and she had great difficulty shedding. The reptile bark appeared to be less drying. With Silver, our new boy, we have used reptile bark so far and damp paper towels for humidity (we are in a dry climate), but as he has just shed and appears to like to burrow I will probably switch to Aspen until he is ready to shed again. I want to be able to find him and he can hide too well in the dark reptile bark, whereas the Aspen is light colored.