Let me preface this by saying, it is not uncommon for me to wear one or more puffy(s) on a 20+ degree day.
With that said, this jacket is just right for cold to moderately cold days spent skiing, mountaineering or for general outdoor play.
While it looks like, and in some ways acts like, a shell–it is not. With breathability and function in mind, The Stretch Nano Storm was specifically built for the start and stop cycle in the mountains. Making skiing a perfect application for this jacket whether you are in the backcountry or riding chairlifts.
It is constructed to be highly breathable–no Gore-Tex here and pit zips galore–insulating with Patagonia's Full Range insulation and has the H2No® Performance Standard shell fabric to keep the wet and cold conditions on the outside.
The fabric has the hand of a softshell and puffy combined, and has exquisite stretch to allow for deep day downhill swimming. My only complaint is it's lack of packability.