Bought a XL, and it was quite small. I usually wear between a L and XL. Also, I did not know it didn't have a zipper. Shipping was also quite slow and they eventually emailed me asking if I had received the jacket. Turns out they hadn't shipped it.

5'11'', 185 lbs, Athletic Build - Size: Large
I originally bought a Medium but had to exchange for a Large. Large fits perfectly and I would suggest sizing up especially if you want even light layers underneath. This jacket has been great for both hikes and nights on the town. Have received multiple compliments. This jacket has also held up nicely in weather as cold at 20 degrees but is also light enough to wear in 50 degree weather.

I purchased this jacket to wear when it gets too cold to bike commute in a hoodie or sweater. It has worked great down into the low 20s and the stretch side panels not only allow for a great range of motion but they also provide just the right amount of ventilation when pedaling uphill on the warmer days. The styling is prefect for a work commute as I can wear it right to a meeting without looking out of place.