I bought a fitted ball cap in the same size of the last one I owned and it showed up very slightly too tight so I searched and found tips I should boil water in a pot with the hat on top of the pot, soaking up the steam for 5-10min to stretch its fibers slightly, then wear it after it cools down and goddamn it *really* worked.
Feels perfectly molded to my head now. Thanks, weird internet advice.