I was never a vest person. I didn't see the point of having cold arms. Then I tried a heavy fleece vest once and was sold. I didn't realize the extent to which keeping your core warm kept the rest of you warm. But the fleece was heavy. The thermawrap is decidedly not, and is just about as warm as that 300 weight fleece. It insulates well and is windproof. Worn with a midweight baselayer, it was enough to keep me comfy in the mid-30s while xc skiing. (My arms were chilly from the breeze when I was moving, but that was an acceptable trade-off for not being drenched in sweat, as happened when I tried wearing a softshell. A wind shell over the vest should do the trick next time). When not moving, throwing a light softshell over it kept me plenty warm. I debated between the down vest and the thermawrap, the usual pro/con of the superior warmth/weight ratio of down vs the peace of mind knowing the synthetic will keep me warm when wet, and am glad I decided on the latter. I get sweaty when active, and always end up with the vest pretty soaked especially when under a shell in the snow/rain. Being synthetic, it still keeps me warm. I doubt the down would hold up as well. All I would add is a zip chest pocket for things too valuable to risk falling out of the zip-less hand pockets.

I ordered this vest thinking it was going to be a bit thicker, but i'm glad it isn't. it fits beautifullly under any jacket or even hoody. the color is stunning. kind of a burnt orange meets copper color. i wish it stuffed into its own pocket rather than the little pouch it comes with. but that's a flaw i can deal with. overall. a great vest for layering.

One of my favorite pieces of insulation, I use this through all four seasons, and it has found an almost permanent place in my pack. It's so light and compact (just bigger than a can of soda when stuffed down) that it's hard to justify not carrying it. Works great as part of a winter layering system, and I find myself wearing it both on the trail (with a light wind shell or hard shell) and at camp (under a MontBell Alpine Down jacket). It adds quite a bit of warmth for it's size, without leaving you with sweat pouring down your arms. Also, I tend to carry it in my summer day packs as a "just in case" insulation layer, where anything heavier would be extreme overkill. Being built with typical MontBell quality (awesome), I've put a couple of hard years on this thing and it's no worse for the wear. Note however that the outer shell is very light fabric, meaning that you should refrain from bushwhacking while wearing it as an outer layer, as it could easily tear on a sharp twig or branch. That being said, I haven't "babied" mine at all, and it has held up really well (better than I expected).

This is the insulating layer that you want in your pack for unsuspected cold weather. It weighs nothing and takes no space. Still, it makes a significant difference when worn under a hard shell, or in a sleeping bag at night. Definitely a good buy.
Although the sizing supposedly has been adjusted for US people formats, I still needed to go up one size to get a comfy loose fit that you want for an insulating layer like this.

I was hesitant about weather or not this would keep me warm but i was pleasantly surprised! Kept me warm without overheating while hiking the routeburn track in New Zealand. This track brought us through temps from 75 deg to 34 deg. I just wore an icebreaker 200 long sleave top + icebreaker ultralight T-shirt under it and an ultralight sierra design isotope shell over. It is Ultra light and packs down so small it's stupid not to take it everywhere. Because i use a down sleeping bag i like to have a synthetic fail safe insulating layer. Montbell rocks!

Expensive, impressive, and a fit to kill for. But having tried this vest in a variety of chilly wet situations on the trail, I can say that I found no discernable improvement over just wearing my Backcountry.com wool jersey and a parka versus adding the vest. The warmth improvement is minimal, in my opinion, but it might just be the edge you are looking for, particularly in your 30-degree sleeping bag at night. Highly packable and of negligent weight. I would not recommend it for wilderness travel of any serious duration, even though the weight is so very very light. It is just too light to make a significant difference for the price.

I did a side-by-side comparison between the old vest and the new version. My results:similar fabric and quality, but the new one ditched the athletic cut for what I like to call the 'patagonia cut', or 'typical american cut'. Translation: the new vest will fit well if you are 20-30lbs overweight.