A baseball cap is a fashion accessory as much as it is a part of a baseball uniform. Caps are worn with virtually any type of clothing and are used to showcase a favorite team, advertise a business or cover up a messy head of hair. Washing a baseball cap can be tricky, because the caps tend to lose shape during the process. Most caps are cotton or polyester instead of wool, so the process is not quite as challenging and shrinkage is less of an issue.
Put your cotton or polyester baseball cap in your washing machine, and wash as you would a regular load, in cold water with clothes of a similar color.
Place the cap on a plastic cap mold or a large coffee can to air-dry, so it will retain its shape.
Wash wool caps by hand in your sink, using mild detergent and a clean cloth. Try not to saturate the cap completely and place it in a mold to dry.