Around here heat can't be avoided, but I've ridden across Nevada twice in 100+ temps. The first time I wore a mesh jacket, and wasn't uncomfortable, but by the time I got back to the barn I was drier than a popcorn fart. Took three days to rehydrate. It could have been serious. The second time I wore a very well vented textile jacket that slowed the air flow but still allowed cooling. Still comfortable, but not dehydrated when I got back. The mesh was in the trailer that was stolen, and I don't miss it a bit. On both trips I drank plenty of liquids. The mesh just wicked way more sweat than was necessary. The idea is to stay cool...not dry. There's no cooling effect when the skin is dry, and when it is dry the body will try to sweat more. Hence dehydration... Keeping dry will feel more comfortable...who likes sweaty clothes??... but it causes more moisture loss. Another thing that should be covered is fluid intake. The first trip is was two large bottles of Desanti every 150 miles. The second was 8oz bottle of Gatorade when stopped to pee, or fuel up. On the first trip I covered 600 miles in 10 hours and didn't need to pee once. The second trip was about 500 miles and about 10 hours and pee'd a lot. Everybody has their own ideas on how to ride in heat. Mine doesn't include a mesh....