When I had a tank I tried the foil on top but it wasn't enough. I had some success with using a damp beach towel folded and placed over 3/4 of the cage top. I would turn it each day, rewet it, and had two different towels I rotated so I could wash as needed. With misting I could maintain the humidity. This worked for me, and I live in a dry climate. Maintaining humidity was the biggest factor in my switching to a PVC cage though. It was a lot of monitoring.
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