Not a wool one, I wouldn’t even try it, but a cotton ball cap that I have and dearly love looks like unwell puppies have spend time on it. I don’t want to destroy the hat, especially the brim. My girlfriend is insistant on washing it, but I’m looking for tips not to kill my trusty fishing hat.
Top rack of the dishwasher, right along with the dishes.
Throw it in the washing machine, and then when you take it out put it directly on your noggin and wear it until dry. That’s the only way to be sure to get it clean and to also make sure that it retains it’s proper shape. Works with wool hats just as well. Carry on.
I’ve always used the dishwasher.
I just wash mine in the sink, with some warm water and a little bit of dish soap, then set it on the back porch to dry in the sun.
Note on the brim – look at the stitching. A cheap cap will only have a couple of lines of stitching across it and the brim is more likely to warp or pucker. A good cap should have a half-dozen or more lines of stitching and will hold up pretty well to washing.
Word to the wise, try and determine if the hat has a cardboard brim or a plastic one. Most decent hats these days have plastic, but you should try and feel it out. If it’s cardboard and you get it wet, it’s pretty much never going to be the same again.
For all methods, it’s the drying that screws it up, not the washing. Get it on your head to dry if you want to keep the shape.
Mr K puts it on a large coffee can until dry.
Oooh, I like this idea. I think I’ll give it a go with a hand wash and see what happens drying it on a form, like a coffee can.
I’ll echo what everybody else said about putting it in the dishwasher. They also sell plastic cap holders that you put your cap into before you put it in the dishwasher. It pretty much holds it in place so it might be something you want to look in to.
We use the 2 lb, 7 oz Maxwell House (which is the only thing Maxwell House is good for). 
Get yourself one of these and throw it into the wash.
The problem I’ve always had with hats mis that the two front panels tend to get all ribbed when they get wet (though I do have the new black-billed polyester hat and I’ve kept it dry so far). This is true even if I got out in the rain and then let it dry entirely on my head.
That’s going to work great if your head is shaped like a coffee can…
I recently washed two caps from Old Navy in the washing machine. Took them out, stretched an elastic hair tie around the brim to keep it curved and stuck it on the windowsill in the sun. They’re both just fine now.
The best way (and only way) I’ve ever gotten a clean hat from a dirty one is I go online to www.whereverIboughtthehat.com, order a new one. Throw old one in garbage.
I was thinking brim arc… 
Wow. I had no idea people were afraid to wash their hats! We toss Mr. K’s into the washer all the time! Just no drying. Maybe it depends on the quality of the hat. His are usually like $12-$15 bucks I think.
Who knows…he has a giant duffle bag FULL of hats. Well over 100. Even though he only fixates on two or three.