Took your advice and went with an XL. Glad I did. I can wear a fleece jacket or a couple of thin layers, such as a wicking shirt, and the jacket is not uncomfortably tight. This is probably my favorite piece of outerwear that I own. So glad I got it.

I bought this about a month ago and I love it. I'm glad I ordered a size up (Im somewhat 'thick'). If you keep moving, this will keep you warm. I carry it on dayhikes constantly, but because it's so thin, be careful if you're going somewhere you may have to go through thick brush with thorns or briars. I got it snagged several times on small thorns and I thought it put a hole in it. No tear was detected, but I won't do that again. I'll wear a thicker shell next time. I wore a Columbia longsleeve wicking shirt under a Columbia short sleeve wicking shirt, and had this over it, and I was warmly hiking in low 40F degree temps. For bike rides, hiking, running...it's great. Best piece of outdoor gear I own, because it performs well, very very lightweight and versatile.