Excellent underlayer. WARM. Fits close.
It fits nicely under my Arc'terx Maverick jacket. I have to hold onto the sleeves to put it on as means one fleecy thing trying to slide over another. While it fits close, it is totally non-binding, has lots of shoulder room and longish arms to keep wrists warm! Only con: I wish the neck were a little bit looser. If you're on the fence small/medium, go medium if you don't like a close necks.