We use very fine napped carpet. They look good, it is inexpensive, and if a snake makes a mess, we simply change out the piece of carpet. We keep plenty of extra pieces with us.

With that said, I have seen people use diamond soft (white recycled paper product, and marbles. I don't like these, because if a mess is made, you have to remove all of the small pieces and replace it. Most of the time, they don't leave the material in the case, and it seems to time consuming to me to have to remove and replace that stuff.

With that said, we leave the carpet pieces in the displays when we store them. (as long as they don't have urates on them, as this creates a foul smell after it has been stored that way for a length of time).

Hope that helps,