Originally Posted by Carbonfiberboy

I've ridden the same passes in the same temperature range with and without a base layer, and NO, a base layer does NOT keep me cooler. What it does, is dehydrate me at a much higher rate. Base layer advocacy for hot weather makes no sense. The base layer is an insulator, just like it is in cool weather. There's no difference. The fact that I dehydrate faster doesn't mean that I get a greater cooling effect. Were that true, no one would wear one in cool weather. The outside of my jersey will probably be cooler than if the jersey were touching my body, but it's not touching. Instead, it's separated by an insulating layer. And of course water evaporates more slowly from a cooler surface. What happens in that both my base layer and jersey become totally soaked to where I could wring water out of them. My skin tight jersey alone feels dry when I take it off at the end of a ride. That's how fast a good technical fabric touching both skin and atmosphere can transfer and evaporate water. Light color makes a big difference, too. I prefer a light yellow. Dark colors are just nuts. Put your hand on a black car and a white car.