Although I have used this as a baselayer for colder temps, I use it mostly for running. It always keeps me at the perfect temperature and lets the sweat evaporate. It doesn't get too cold here on the Oregon coast, but I stay comfy with this as my only layer while running with temps in the low 40s. And the bright pink is nice and visible on the road! I'm 5 ft 6 inches, 135 lb and normally wear a small or medium --the medium is perfect in this top.