Confortable + Light + Warm
Very good jacket. Extremely comfortable, warm and light. Very good for hiking: fits everywhere. Once you reach to the summit just put this baby on (and an outer shell) and you are golden.

Top notch!
This has become my favorite layering piece, hands down. I've worn it under my Beta AR with only a Smartwool baselayer, and have been warm in temps dipping into the upper teens while walking the dogs. It's ultra light and warm, and you forget you have it on after just a minute of wearing it. I highly recommend the Atom LT.

I love this little guy - Highly recommended
It took me a while to figure this jacket out. By no means is it a jacket that you could ware to a Bears or Skins game in December with a shell on and be warm just sitting there. I think Down really has a hold on that. Where this jacket shines is when you are moving, be it cross country skiing, hiking, hunting upland game, or backpacking in the winter months. It is far warmer than you would expect as it really is crazy light. If you don't team it with the right base layer you will be sweating bullets. This jacket truly is a midlayer. It fits like one also. If you think you are going to get a big sweater or fleece under this jacket in your normal size you are mistaken. I am 61 200lb and the XL from Arcteryx has always fit me like a glove. The Atom in XL is fit as a midlayer (you can get an R1 or covert zip under it) but its thin enough to be worn under a shell. This jacket with my Arcteryx Theta is my new go to combo. But again if it is supper cold you may have to go with a beefier fleece under the shell to stay totally warm.

Light & Warm
This jacket is amazingly lightweight and is surprisingly warm. Can be worn as a jacket on a mild winter's day here in the Northeast, and is great as a baselayer for wearing under a shell for skiing. I have also used it for traveling around the world, and it can pack down into a very small space in one's hand luggage.

Lightweight and perfect layering piece
From the moment I tried this on I was sold. Very nice fit, lightweight, and warm. Perfect layering piece and works worn alone too. Fairly tight fit so try on first. Only negative is there is no drawcord. Otherwise, great jacket!