HOGGABEE This hat is convenient for use in the sea or river. Originally designed for surfing, the string is designed to detach if pulled too hard, preventing it from tightening around the neck, which provides peace of mind. The upper inside is made of wetsuit material to protect the head. The brim has a firm, solid material to maintain visibility even when wet. The sides and back are soft, and the sides can be secured with buttons. I believe it is a water-repellent material. It measured about 53cm, but please understand that there may be some error as it was measured by an amateur. It will be folded small and sent directly in a paper bag, so please be aware of this. Olive green outdoor hat with mesh side panels. - Color: Olive Green - Design: Mesh side panels - Adjustment: Adjustable strap Thank you for looking.