Sweat, body oil and dirt can stain and discolor a baseball cap, leaving it looking dingy and smelling foul. Baseball caps made of polyester, cotton and twill are machine-washable, but vintage caps and those made of wool require gentle hand-washing to maintain their structure and appearance. Always check the tag on your cap for specific washing instructions.

Apply a prewash spray to any stained spots on a machine-washable cap. Let it sit for at least five minutes. Wash the cap in the washing machine on the gentle cycle using cold water and regular laundry detergent. You can add other garments that require the same washing instructions, but do not use bleach, regardless of the color of the cap.

Mix a solution of warm water and a few drops of laundry detergent in a bucket. If the hat is wool, use cool water wool shampoo instead of detergent. Dip a white washcloth into the bucket and wring it out well. Scrub the interior and exterior of the cap with the washcloth until the cap is clean. Scrub gently – especially on wool hats – to avoid damaging the fabric. Rinse the washcloth often in the bucket of soapy water while washing. Rinse the hat under cool running water to remove any soap residue, then blot the hat with a towel to remove excess water.

Reshape the cap with your hands after washing. Set the hat on a head-shaped form – a canister, coffee can or upside-down saucepan, for example – to maintain its shape while it’s drying. Dry the cap in a well-ventilated area away from direct sunlight. Do not dry baseball caps in the dryer.