Richardson recommends NOT washing their hats. Instead, they recommend spot cleaning. For the outside of the cap, take a damp rag, not using any detergent and gently scrub the soiled areas. (Please note, sweat stains are to caps as tattoos are to people; they're unique and very hard to remove.) For the cap's insides, use a damp rag along with a little laundry detergent, especially on the sweat band, and scrub away. Once your arm is tired from scrubbing, get another damp rag, without detergent, repeat the scrubbing process and then let your cap air-dry.