I have a MontBell Down Jacket in Large and it has a slim fit. This vest is much more roomy. I returned and may try a medium. Good quality and lightweight just like the jacket, though.

I thought it was all talk.....super light, super warm, very compacting. Man was I wrong! Literally this is the warmest vest I've got. It's just as warm, if not warmer, than my puffy marshmallow vests but is a lot lighter and compacts down to the size of, well less than my fist. They fit true to size. This is a great find if you're looking for something well made with great qualities and function!

This was the perfect addition to my layering system. I'm a wilderness guide so I want to be wearing the best stuff out there. Looks like I found it. This vest allows me to push the limits of my summer bag. It packs up to almost the size of a red bull can. It's toasty!

Very light vest. 6 oz vs 16 for most down vests. Meant to be worn under another garment but fabric is heavy enough for outerwear unless you are bushwhacking or otherwise getting stabbed by branches.
Has big pockets that are inside insulation. Overall very satisfied.

Nice jacket and super light weight. However, the fit was a bit larger than expected so I'm returning. I already own the MB Extremely Light Down Jacket which is pretty form fitting in a large--this was a little more (too) roomy for me in the torso.

I received my new vest a few days ago. It's better than I expected. Extremely light weight layer for all but the most strenuous activity where wicking moisture is the most important function. It was initially purchased for an ultralight summer backpacking layer but I'm now considering it for all my winter activities also.

Yes, yes, its super-uber light and packs up incredibly small. I was just worried about how warm it would be. Well, its also super-uber warm. I started wearing this everywhere to see how well it worked - going to work, walking the dog, light hikes, strenuous hikes. With a couple light-midweight layers underneath it kept me warm and regulated temperature great. On anything but the easiest walk I found myself unzipping it because it was so toasty. Found its cold limit one night on a walk at about 15 degrees with two layers underneath. Great for stuffing in a pack in case you need it when out hiking, snowshoeing, skiing. Easily fits under any jacket/shell for layering.
I'm 5'11" with an average build and the Large fits perfect for layering underneath and/or over.
Minor cons: no zipped pockets, no drawstring waist
Bottom line: Warmth you'd expect from a down vest but because of how thin and light it is, its incredibly versitile.

This is my first piece of down clothing and I love it! It's super light and keeps me nice and toasty. I purchased it with the intent of using it to extend the range of my 40 degree Marmot Atom sleeping bag for spring and fall camping. I've slept in it once at temps around 25-30 degrees and stayed very warm. Other than that, I've worn the vest around the house and around town and it's always keeps my core toasty while the lack of sleeves keeps me from getting too warm. I consider it one of the best gear purchases I've made.

This vest is great. Very warm. So light you don't know you have it on and it packs into a tiny size. Totally satisfied.

Very light, surprisingly warm, good looking. Good fit, snug around the neck. Very pleased with this.

WOW!! super lightweight and very warm, perfect for layering. Montbell does it again.

This past weekend made it out to Brighton for an early powder day and it was friggen cold. Broke out the stuff sack (which is about the size of a beer can when squished) out of my pack and didn't so much as cringe the rest of the day. Its so friggen handy to have in your pack. You never realize its there since its so light, its super small, and its great at warming your core. I'd give it 5 stars if I didn't feel like people were snickering at me when I put it on. It does look a bit funky, but under a soft-shell... who cares.

This thing packs down as small as an apple, and is super warm. I used it on the PCT for a couple weeks and it worked great for when I needed just that extra layer. It's always hanging out in my ski pack, ready for when a storm blows in. It even gets used as casual wear, but I am not sure if I could recommend it too much. Biggest downside is now they use a zipper, mine is way cooler, and has snaps.

He loves it and is already wearing it around the house, great while working on his computer for that extra warmth but it's really for backpacking.