Water proof and packs down small of flat if you prefer. Back of brim slightly larger to keep water off neck/ upper back. I like in conditions where it is to warm to use a Gore-tex jacket but still want some protection. Also great when conditions are just cool enough for a rain jacket, but putting up the hood then makes it too warm; jacket and hat work great in this scenario. My brother is now envious and wants one as well.
Michel G Thank you, Robert. With Xmas coming on, your brother might have one at least, I imagine !
ROBERT A I will do my best to try and remember to measure. Until then, approximately 3.5-4in front and sides, 5-5.5in rear.