Mil-spec poly/cotton boonie hats will give you maximum protection against the sun. They also have side vents for breathability along with branch loops and a chin strap. This is the Camouflage Pattern that the US Armed forces used in Operation Desert storm in the earlier 90s!
MADE TO GOVERNMENT SPECIFICATIONS
SCREENED SIDE VENTS
AVAILABLE IN SIZES: 7", 7 1/4", 7 1/2", AND 7 3/4"