Combining the microchannel construction of the MicroTherm™ Down Shirt into the lining of this fully waterproof and breathable shell rated to 20K/20K, makes it possibly the lightest, warmest waterproof jacket on earth. Patent pending. This jacket excels in cold, wet environments and has been vetted by our First Ascent guide team in the worlds harshest conditions such as Everest and Antarctica. Highly packable. Across the board, this piece was the alpine guide's personal favorite, hands down. "A lightweight, high-performance piece that keeps me warm and dry on cold, windy and wet days. You don't generally want to be out in those conditions, but sometimes the mountains have other ideas. This jacket was made for those days." - Melissa Arnot