I recommend the Boonie Hat; especially in the warm weather.
It is a wide-brimmed hat that is better known as a Bush Hat. It is used for various reasons; one of the many reasons is for military use. It was first used in the U.S during the Vietnam War. There are quite a few prints and colors to choose from.
It will definitely keep your head protected from the sun. It allows an extreme amount of shade for you to keep cool. As far as the material, it is a matter of preference. When the Boonie Hat was first introduced it was mainly made from excess material from parachutes. Some prefer rib stop; while others like a nylon blend. It really depends on the reason of use.
Fishermen are often seen wearing them because of the loops around the base of the hat. It is a great place to store your lures. If you are looking for full coverage in the hot sun, this is a perfect pick. There are usually vents that allow air to get to your head. The best part is you can adjust the hat to how tight you would like it on your head. Try it!