To clean a fitted hat, such as a baseball cap, run the hat through the washing machine on a gentle cycle in cool water or wash the hat by hand. Some people attempt to wash their caps in the dishwasher, but manufacturers warn against this to prevent voided warranties.
Washing a cap in a sink or bathtub is the easiest method next to using the washing machine.
Prepare the basin
Fill the sink or tub with dishwashing detergent and lukewarm water. Use a sprayer nozzle to generate more suds if that is desired.
Wash the hat
Scrub the hat with a sponge or soft cloth, then rinse it in cool water. The hat can be pre-treated for stains if necessary. Hang the hat to air dry completely before wearing it.