Snake bedding?

I recently acquired an eastern kingsnake and currently have him in a cage with paper towel substrate. I want him to have a more natural looking home. I know that he is more of a forest species and I was wondering if their is a safe kind of mulch I can use as a substrate. I realize that some mulches have additives and insecticides added to them. Are their any fine-grain all natural mulches I can use that is safe for my kingsnake?