[not sure if this is the best place to post this, but here goes]
There have been a number of posts on the forum in regards to the sizing of montbell stuff. I did as much research as I could and bought a U.L. Thermawrap vest in size M. As it turns out, it was way to snug for me. So I bit the bullet, ponied up the extra shipping costs, and ordered a L to up size. This turned out to be the perfect fit. Hopefully I can help some others out w/ the same question and provide a better benchmark to the thermawrap sizing question.
Here's my stats – 155 lbs, 40" chest, 32" waist, 16" neck.
Here's what the medium looks like (too short, snug in the arm pits and waist. Vest rides up too easily)

And here is the size large. (perfect fit)


