Stretch an old hat that is now too small, or a new one that is one or two sizes too small, so that you can wear it comfortably. Many hats such as baseball caps, fedoras and beanies are made of fabric that, when wet, shrinks or stretches depending on how you dry it. You can use a specific procedure to stretch your hat by making a form that is the same size as your head.
Measure the distance around your head from the middle of your forehead to the back of your head. Place the end of the tape measure in the middle of your forehead again, but bring the tape measure over the middle of the top of your head to the base of your skull. Take note of these two measurements.
Roll up a thick towel, or more than one towel, in a tight, round tube. Measure the distance around the rolled towel (s) to tube and wrap more towels around it until it is the same circumference as your head. Wrap twine around the rolled towels and tie the ends together to keep the towels rolled tightly together. Wad up another towel into a ball that is the same distance across as the measurement across the top of your head. Tie it to the top of the towel roll with the twine.
Fill a bucket or the sink with warm water, add a 1/2 cup of mild clothing detergent to the water and stir it around with your hand to evenly disperse it and help it dissolve. The detergent helps to soften the fabric to make it more pliable.
Submerge the hat it the water for 30 minutes to make sure to completely soak it. Remove the hat from the water and let the excess water drip off.
Stretch the wet hat over the towel form you made and wait 24 to 48 hours for the hat to dry and for the towel to soak up the water. Place the hat on the towels in front of a heater, no less than 2 feet away for safety. When the hat is completely dry, it will have stretched to the size you need.