Heres a thought: Pack a lightweight umbrella. GoLite (golite.com) makes a nice light one called the GoLite Dome, which sells for $25 and weighs just eight ounces. Its like carrying around your own shady patch!
Otherwise, I think youre on the right track looking for loose cotton clothing. I dont think theres anything magic here; good-quality cotton tees such as L.L. Beans Carefree T-shirt ($12; llbean.com) would work fine. I know, I knowcotton doesnt belong in the outdoors. But its very cool and comfortable in hot weather. Just be sure you have a dry change in case you sweat through and the weather cools. I also like Patagonias Capilene 1 T-shirt ($36; patagonia.com) in hot weather. Its super-light, wicks and dries well, and works as a base layer for chilly weather.
A good source for hot-weather clothing is the Sunprecautions.com site. It carries lightweight, high-SPF items such as the Safari Shirt ($80) or Cargo Pants ($80). I also like Ex-Officios clothes in hot weather, such as its Reef Runner shirt ($60; exofficio.com).
I havent heard that hemp clothing offers any particular advantage, but it very well might. Try Hempest.com and take a look at the Hemp Button Down Shirt ($68).
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