This is an ok base layer. The trouble is that the wind blocking stuff is right up against your body, so you sweat, and kind of get chilled. Its better with another base layer under it, but with Castellis notorious tight fit, that might not be comfortable.
I had to return one, as the collar stitching ripped (does Castelli think cyclists are microcephalic?). BTD replaced it, no problem. But I went up a size, and its still pretty tight. XL now, and Im a pretty average sized guy. So go up a size or two.
Great for buffering wind for cooler rides. In the winter I will often ride 40 to 50 degrees. With this undergarment I no longer need a jacket. Moisture is wicked so it does not get heavy or uncomfortable. I normally wear an ultralight rain jacket over my jersey with this undergarment beneath all. It forms a good barrier with layers that can be removed if the sun comes out. KOP...Keep On Pedaling!