CUSTOM S Hi Sara, I bought the regular, I wear a smaller size in hats. It has a nice adjustable strap on the back to make bigger or smaller. I am able to put my hair through the back like a pony tail and that helps me in the heat. It is a very light weight hat but seems to do the job. I really like the venting on the sides. Hope this helped.

Zack W The Head Circumference for the regular would be: 21" - 22.1/4", and of the large: 23.3/4" - 25". Enjoy it! Zack.

Zack W This hat isn't water proof. Enjoy it! Zack.

CRAIG K I haven't worn the hat in the rain, but would assume it is not waterproof as it is vented on top - the internal part of the brim is made from some type of foam so it floats if dropped in the water - this is a great warm weather cap with plenty of ventilation - my husband had purchased the men's version, which I liked so much that I decided to buy my own - sunnysports was also excellent to order from... Mary