I have a big head to begin with. I'm talking 7 3/4 to 8 depending on the style of hat, how long it's been since my last haircut, and the amount of fat in my face which varies considerably. Because of my varying head size and the fact that I like to wear fitted wool baseball caps, washing them is a concern. Perhaps it's a concern for you as well.

Therefore, here's an article on how to wash a cap. The recommendation (short of not washing it at all) is a little bit of water and Woolite. Dishwasher baseball cap racks be damned!

The option recommended by New Era is to not wash it at all. They recommend a little Spray and Wash on a damp cloth to clean that sucker. I'll let you decide how much risk you're willing to take.

One thing I'll point out that's saved me and my varying head size is that last tip of breaking the plastic sizing in the 59fifty to make the hat just a tad bigger. Works like a charm, though I think all three of my fitted caps currently have all the sizing completely broken out... Dumb, fat head.