I have a few that I like to wear but they are getting a bit dirty....I know washing them in a washing machine isn't the way to go lol.
I put mine in the dishwasher. Top rack. Works great.
I sympathise with you on this question. Some of the brim stiffeners are not of a material that takes kindly to water and some hats are anything but cheap. Wrap a towel into a ball and insert it into the cap so the outer material is taught. Using a good quality car shampoo spray the cap, work it in with a soft brush and let it sit a while. Then wipe off all residue with a warm soft white cloth. Do not use microfiber as they can bleed color. For grease or oil stains, treat the area with the stain sticks you use on laundry five minutes before cleaning.I have a few that I like to wear but they are getting a bit dirty....I know washing them in a washing machine isn't the way to go lol.
I HAVE used the washing machine with no problems. I guess it depends on whether the front stiffener is cardboard or plastic.