I live in the frozen tundra of Minnesota, and was looking for a little bit warmer, yet not overly bulky jacket. I received this coat a few days ago, and temps have been in the teens and twenties. So far this coat has been perfect. Probably would need to add a shell for anything sub-zero, but fine for anything above that. I would say that overall the coat runs small. I am 5'7" 150lbs, and I usually teeter between small and medium sizes. Read an external review that said this coat runs small, so I got a medium. Torso length is a touch long, and a touch wide, but not bad. Arms are plenty long. But I think a Small would have been too small. So order accordingly. My only complaint of this coat is that the neck/collar is a little more loose than I would like. Not terrible, but I would prefer it to be snug against my neck to avoid seeping in cold air. This is the first Rab product I've owned, but I it appears to be a very well made jacket.
You know if its Mammut its quality. The medium fits me great, I'm about a 39 chest. No chills when I'm up high in the early morning, though, I haven't taken it below 30 deg yet- that will happen in another two weeks. I love how light and soft it is- hardly know you've got it on apart from the fact that you feel like an oven in about 5 minutes. - See more at: http://www.moosejaw.com/moosejaw/shop/product_Mammut-Mens-Broad-Peak-Light-Jacket_1706809_10208_10000001_-1_MEMBER_RELATED#sthash.2XIIX4ru.dpuf