wood

[decensored]

uh oh, here goes the debate...

Namely Cedar and hard woods are toxic.
Aspen and Cyprus are safe, but according to many experienced keepers kiln dried pine is safe. Even still, I don't like the idea of risking it.

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to make my rack
sorry i thought i put that in the op

Melamine is your best bet, but any wood is fine as long as it's sealed and finished properly. Your biggest concern is where the open space is against the top of the bin. As long as that is sealed and finished properly it'll be fine.