I wore this on a difficult 4 hour hike in Maine yesterday under the Windswell running jacket. The hike involved summiting 3 peaks - very windy and chilly at the top of each peak but very warm below the tree line as we were climbing up. This baselayer would get sweaty as we were climbing and I’d take off the jacket, then by the time we had summited and come back down it was totally dry again!!! So awesome not to have to deal with a cold clingy baselayer in varying conditions like this. For sizing: I’m usually a medium in Zoot cycling/tri gear and a small in running gear. The medium was very fitted so I sized up to a large and it’s perfect.