If you take only one hat on your long summer adventure of backpacking and trekking, it should be the Arroyo Bucket from Outdoor Research. With UPF 30 construction and lightweight, breathable fabric, you'll be protected from the rays. Reversible style lets you switch from subtle to spunky.
Reversible/Plaid: Plaid side made from cotton; solid side made from Supplex nylon
Reversible/Solid: Sand side made from linen; Khaki side made from Supplex nylon
Supplex nylon is breathable and fast drying, holds its shape, and resists fading
Lightweight, breathable fabric wicks moisture
SolarShield construction with UPF 30 for protection from intense sun