170lbs, 5'10". 43 inch chest.
Large fits perfectly.
It is a great long sleeved undershirt, in reality. The odor proofing allows you to merely rinse it out, hand wring it, and with just a slight breeze, you can have it ready to wear in a very short, low tech time.
It's a great base layer for winter fishing, or just hanging out.
It it is easy to snag, usually not a problem if worn as a base layer, and that's the only reason I didn't give it five stars