Paper towels or unprinted news paper. Personally I have no humidity issues at all in my tubs. As much as I like using cypress ive found my tubs hold humidity so well its completely unnecessary for me. In my bigger cages (or back when I used glass tanks) I use cypress. In my tubs I get consistently good humidity with a water bowl. I do live in a more wet climate then some, so obviously your mileage may vary

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