I have worn this as a base layer for skiing as well as other outdoor activities in the cold (teens to lower 30s). I have stayed warm but the material breaths appropriately once i'm inside and it warms up. I'm 5'8", 153lb and the small was too tight. I exchanged for the medium and the fit was spot on.
The thickness of the top is insufficient should be thicker and better support for the upper back and shoulders