It is the humidity or lack thereof that makes you uncomfortable in the heat. We've been hot out here for the past two weeks and I've either worn my 6yd casual or my 13oz 8yd wool. Either one breathes well in the hot 95F+ weather. I can get away with wearing my 16ozers early in the A.M. or early evening when the temps get into the 60'sF. Even with a slight breeze the 16ozers are a tad much for the really hot temps/days.
Nulty