Wool hats are known to shrink slightly in hot water. Because of this, manufacturers usually suggest they are washed cold. However, if a wool hat is too large and is not adjustable in any other way, shrinking it may be the only way to make it fit. Whether it is a homemade, knitted hat or a manufactured wool hat, it will shrink in hot water unless the wool used is a special, shrink-resistant type, such as "superwash" wool.
Fill a large pot or pan with warm water. Usually water straight from the hot water tap will suffice, but alternatively you could boil cold water and leave it to cool for ten minutes. As a general rule, hotter water will result in a more extreme shrinking effect.
Submerge the hat in the water, using tongs or a wooden spoon. If the hat in question is a baseball cap, make sure you don't submerge the bill.
Place the hat on a balloon or ball, the size of your head, or put it on your head, and allow to dry. For more extreme shrinkage, place the hat somewhere by itself to dry, and dry it with a hair dryer.
If colours in the hat start to run, rinse the whole hat with cold water as quickly as possible, and dry with a hair dryer or hand dryer.
A similar shrinking effect can sometimes be achieved by wearing the hat while showering, and then allowing it to dry naturally afterwards.
Be careful of hot water: don't get burned. Be extra careful if allowing the hat to dry on your head. Check the temperature of the water before placing the hat on your head. If wearing the hat while it dries, watch out for running dyes as these may drip onto your clothes and stain them.