Actually, I find the castelli mesh jersey, like this one, keeps you cooler than the UA option when wearing a tight fitting race cut jersey. The UA option worked well with a tshirt, but I'd never wear a tshirt on a road bike. That said, I will still opt for no baselayer 99% of the time. Almost all of my jerseys are race cut and do a fine job of wicking away sweat and keeping me cool. Wearing a baselayer with them, seems to just keep the sweat on you or between the two layers.