It's called Damp rid.

I get the ones that come in a bag form that you can hang on a railing in your closet.

I use it in my apartment where my rosies are located, it works great. I live in statesboro ga where the humidity can get up to 80%. I replace my damp-rids about once every 40 days or so, whenever they are full.
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~Justyne Dickson
www.eboas.net