One of the biggest problems when it comes to washing baseball caps is that the hats shrink. Other dilemmas include a misshaped hat or a broken brim. With careful attention to a few easy steps, washing a baseball cap can be successful.
Start by looking at the materials of the cap. Most new hats have a tag with washing instructions, and most newer hats are made with a plastic brim, which is safe to go in the washing machine. If your plastic-brimmed hat is cotton, a cotton mixture, or jersey knit, spray dirty or stained areas with a prewash detergent. Simply place the hat in a cold water wash, even with clothes as long as they are of similar color.
If your cap is older, the brim is likely made of cardboard and thus should not be put in the washing machine. Grab a washcloth and wet it with water and a small amount of mild detergent. Test a small area on the inside of the hat by rubbing the cloth. Rinse with a different cloth, wet with water. Let the area dry. If there is no color change in the fabric, use this technique for the rest of the sweatband, or other soiled areas.
Wool caps need to be hand washed. To do so, use cold water and a mild wool detergent. Do not scrub as this could affect the fabric fibers. Rinse the hat in cold water and pat dry the hat with a towel. You should reshape your hat once toweled off by air-drying the hat on a coffee can, or if you want a perfect fit, let it dry on your head.
Some people suggest washing baseball caps in dishwashers, but err on the side of caution and first try using your washing machine. Dishwashers can melt the plastic brims.