"you'll probably get better wicking and cooling performance from a good quality, summer-weight base layer than from a more conventional shirt."
But wicking that moisture away, rather than having it sat on your skin to conduct away heat before evaporating, will probably mean hotter.
So better wicking, yes, but if you wick the moisture away that may impede the better cooling, as may being too close a fit to allow air to circulate under it.
Wicking moisture away is primarily a comfort thing, but if your comfort is best served by being wet (to cool you down) it may be a bit of an own goal. At least until the clouds roll over the sun, when you'll be glad to be drier...
Pete.
Edited: 30/05/2012 at 13:30