It was hard to believe while I was wearing this shirt that a fabric that you can see through can be wind resistant and as warm as it was. I was out running in the mid 50's and if the sun poked out I had to unzip and roll the sleeves up to keep from overheating.While getting ready at the car the wind was cutting through my tights and shorts and made me think I may need a light undershirt on. When I took my jacket off to do this the wind whipped up a bit and I didn't even notice it on my upper body while my legs felt cold.Based on how warm it felt I can understand why the more expensive running specific shirts have vent mesh even though its the same super lightweight fabric.
I bought shirt for running and it's kept me warm down to about 35 degrees. I get cold easy, so your mileage may vary. I run 30-35 miles a week mostly on the pavement. This is my favorite shirt to run in when it's in the mid-40's. It doesn't smell after a week of running either. Which great, because I hate doing laundry and don't want to smell like a gym locker.My only complaint is how little is exposed when you unzip it (that's what she said.) The zipper isn't as long as ones found on some other Icebreaker shirts. However it's a pretty light fabric, so it doesn't matter too much. I highly recommend this shirt for any outdoor activity.