I use a very thick layer of peat first (we use use it for our horses too) and it takes away all the smell in my terrariums and it also help keeping the humidity up. Then on top of that, I use Swedish Pine Bark Mulch, non toxic and non smelling. So its not the same type that you sometime can read about that has a strong smell and that is not suitable for tortoises. Here is a link to a previous discussion http://www.tortoiseforum.org/thread-28140.html#axzz29P1N1HxN