Here's a link to an interesting article by Diana Crane. It talks about the social meanings of hats at different periods in time. For example, hat a man wears out in public would represent the status of his family, where the woman's hat was more individual, and allowed for individual style preferences. I never thought of that! I won't paraphrase the article here, but it looks like it would be an interesting read for anyone wanting to learn about the history of hats.
http://www.press.uchicago.edu/Misc/Chicago/117987.html
http://www.press.uchicago.edu/Misc/Chicago/117987.html