Ultra thin puffy
I got this to replace fleece for layering under a ski shell. It's much more compressible and a lot warmer since it's really wind resistant. It could stand on it's own as outerwear in pretty bad weather, as long as you keep moving.
Nice tough-faced fleece up the sides and under the pits lets out just enough heat and moisture that you don't feel clammy during exertion in cold weather. Nicely placed, warm pockets. The collar is not bulky and is kind of short compared to some fleece jackets. This makes it nice when layered under other shells with collars. The cuffs are very low profile spandex-like material with very little bulk. Jackets slide over the sleeves very easily because there is no velcro tabs to snag.
I had avoided Arc'Teryx for years due to the price being high and the manufacturing being moved overseas. So far the fit and finish seems very high quality. I still think the stuff could be priced 5-10% lower, otherwise I'd give it 5 stars.