I use eco-earth expandable dirt, you put it in a bucket of water and it will expand enough for a 40 gallon breeder tank. It is not too messey, and it will hold humidity very well. I did not like the repticarpet as it is terrible for humidity, and I have always had stuck sheds, but I always had that problem with aspen too. I guess it is all about personal preference, and what you can make work for you.