My hats have mold

[MCS]

So today I went out into the sunroom at my apartment. It's like a screened-in porch except it has closable glass windows so it's really sort of a less-insulated, more-ventilatable room of the apartment.

Anyway, my baseball hats are growing mold on them. (Also a couple of my older books that are out there have something that looks like dust but I think is mold.) I suppose this is because the insulation is imperfect especially considering one of the windows got broken and duct-taped up a about a year ago. So I think the humidity got to them.

Any advice on if/how I should clean these hats?