This jacket has served as an underlayer primarily for me and I have yet to get cold while wearing it beneath my Arcteryx Beta AR jacket. I make frequent trips to Rocky Mountain National Park and have sat comfortably in windy, -20ish degree weather. I have yet to go much colder than that, but I often find myself sweating in this jacket while moving. Initially, i was not a huge fan of how thin this jacket is; it just doesn't feel as packed as some other puffy jackets. It is water repellent, and seems to hold it's insulation properties very well when damp. When I say damp, I mean that I have ridden my bike in the rain with only this jacket on (because I wanted to test it out) and although rain seeped in and it is not wind proof, I stayed reasonably warm. It has become damp while ice climbing as well, but I stayed perfectly warm with it on. The jacket is long enough to accommodate a harness without slipping out, and the hood fits underneath a helmet (or over if you swing that way) well.