i was using aspen for my other snake and i found that it does not hold humidity at all. especially here in colorado where it is not very humid! i now have prince on repti-bark which is what he was on before. but i'm finding that as far as i have had it, it does not hold humidity as well as i would like. i was wondering what substrate is the best? Repti-bark, jungle mix, eco earth? oh prince is a ball python (: