I use coconut bark as a substrate. I like it alot. It holds humidity very well, easy to spot clean, it's non toxic, if they accidentally eat some it doesn't harm them, they can pass it through. To keep it moist I mist the cages with water making sure some of it lands on the substrate.

Only thing is you can't plant in it, but I find it easier to use potted plants anyway...
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Lisa

1.0.0 P.m. grandis (Linus)
4.3.0 P. standingi (Toby & Kona and their 5 babies)