
The first thing I grab for any long day outside in wintry conditions. It is soft, stretchy Polartech. The shoulder straps are not too tight or wide, so I don't notice them under a heavy pack, nor do they restrict movement when ice climbing. The torso is long enough to tuck into pants (or the also excellent Run Don't Walk boxers) and doesn't ride up. Wicks sweat away from skin. Really, it was the find of the season for me.
The top runs a little large (I wear a size 8 normally, and I have the small). If you are bigger than a B cup, this will not give you enough support to double as a sports bra.