Fireproof safes have a double wall with an insulating material in between. During a fire this material hydrates to keep the temperature down inside the safe. But that causes everything in the safe to be subject to very high humidity levels. Not good for mint stamps.
Thanks for the replies; I use the silicon desiccant packs in the bottom of my current safe to help control humidity; although it is strategically located as well in a room with a return air and a register over said safe; best I can do in SW Florida.
That said, looking for models/makes of safes more tailored towards books and paper.
I've actually thought about simply turning an existing closet in to somewhat of a "safe" room by installing a metal door as well, but prefer a safe.