I do a lot of physical activity (exercise, hiking, etc.) and synthetic is the only way to go. Cotton clothing SUCKS for those purposes. A lot of companies now make synthetic workout clothing, easy to find both the nice stuff and cheaper end.
"caleda" (swiss) makes a line called 'just feel' made out of tactel and elastane; "jil male underwear" (france) makes some very good synthetic fibre ones as well (made out of modal and elastane but not sure what modal is or if it's french for something); "jimz skinz" (canada) makes a nice synthetic line as well