I've been on the look out for a truly breathable UL windshirt for some time now, and I'm happy to say I''ve finally found one. I was passing through my local running store and came across one by Nike called the impossibly light running jacket. I'd agree that its impossibly light for a jacket that you can actually run in. Just from a quick breath test in store, I'd say it's just a tad less breathable than pertex equilebrium which has been my favorite thus far for use in high output activities like backcountry skiing, running and hard uphill backpacking. But my equilebrium shell is 7.5 oz, this one is 3 oz. I just had a quick look at the jacket in store and tried on my normal size medium. The chest and shoulders were def designed for scrawny runners, so I found it too constricting. I found a crazy magenta colored men's in size large for $40 on eBay, so I've got one on order. I've gotten pretty picky about windshirts, and I have too many already, so not sure if I'll keep it, but I thought it was worth a try. since I really haven't found anything close to this breathable and light. Based on some other threads, this might be a little more breathable than some people prefer and probably more than Nisley's ideal cfm, but for me it seems pretty spot on. Sizing is a little questionable and the hood ain't great, but you can't have it all. http://store.nike.com/us/en_us/pd/impossibly-light-running-jacket/pid-10264497/pgid-1488171?k_clickid=93ed2dca-7f2d-4617-af5d-bebaf724a81c&cp=usns_kw_pla!g!t!nobr!&k_clickid=93ed2dca-7f2d-4617-af5d-bebaf724a81c&kpid=10264497-00675911647011 There's plenty of these for sale online right now and still a couple left of the progressively gendered magenta in size L.
