How easy is it for a cardboard head to mold?

I don't live in a very humid area, but I'm still very worried because I don't want to redo the entire thing after a few uses.

If I made the head out of mostly EVA foam, with maybe some reinforcements inside made of cardboard - would it still mold as easily? Will everything be fine as long as the cardboard is covered by the foam on all sides?

If it helps, the head itself won't be touching mine much, I'll make seperate reinforcements inside entirely out of foam for my head to go in. (unless I can use cardboard?? im very new to cosplays so sorry lol)