I bought this to use primarily as a mid-layer and it works great for that. This jacket alone is warm down to about 30 with just a tshirt underneath. It is not windproof since the sides are a breathable, stretchy fleece. It is very lightweight and does not limit mobility at all. I'm 6'1", 170 lbs and a large fits perfect. I like MH jackets because of the slim fit around the torso and waist. Wearing this under a shell for a day in the backcountry or at the resort in a great combo. It packs downs really well which is nice if you need to stuff it into a pack for a long hike when body temps rise.