They keep you cool if you sweat a lot. they keep cool by being damp with sweat. or you can pour water on you with shirt on and they stay damp for a bit. they do dry fast so have to do it multiple times a day. I wish a company would make them out of light weight Lenin or Cotton becuase I have an allergic reaction to the nylon. I have lived with the allergy most of life, first realized in Army with Polypropylene. But older I get the worse the allergy gets and will have to go back to the old fashion round hats with towels hanging off back. Same with all my favorite fishing shirts that I love because most of them have at least 50% nylon. Going to have to spend the $$$ on Lenin but the problem with Lenin is that it doesn't protect against UV rays as well. I love the lightweight hood but it just doesn't work with my allergy to nylon.