You can shrink a cotton hat that is too large to fit properly. A cotton hat is easy to shrink, and shrinking a cotton hat requires just a few basic household appliances, according to Made Man.
Fill a tub with hot water
Fill a bucket or small laundry tub with water as hot as you can make it. Hot water shrinks cotton fibers. Just put enough water in the tub to submerge the hat. Made Man points out that the hottest water from a home appliance comes from the dishwasher. As an alternative to a tub, put the hat on the top rack of a dishwasher without soap and run it through a hot cycle.
Dry the hat
Put the hat through a hot dry cycle on the dryer. For a moderate amount of shrinkage, choose a low or moderate heat setting. For a significant amount of shrinkage, put the hat through the dryer on the hottest setting. The heat causes the cotton to constrict even more. If it is sunny and hot outside, hang the hat on the clothesline for additional shrinkage and a fresher scent.
Try on and repeat
Try on the hat after it is dry. If it is still oversized, repeat the hot soaking and drying steps until it fits properly.