Since 2011 I’ve owned around two dozen windshirts, and while a third of those were for larger reviews and garments in which I didn’t have an inherent interest, this still amounts to an extravagant total. As of today there are only four in regular rotation. In the same period I’ve had at least the same number of fleece pullovers, vests, and hoodies, including half a dozen items in current use, on top of a couple active insulation pieces. I could, by contrast, cut baselayers down to two or three pieces without issue, and gladly go the whole year with a single hardshell.
All of which is to say that the task of additional weather protection for on the move is far more complex than any other. The most relevant question is thus which items provide for the greatest range of use/comfort, and why. Not only will versatile items better trim the closet, using generalism to frame our inquiry makes for more incisive answers.
I call wind and mid layers, which collectively are generally used for added protection while on the move in the backcountry, action layers (nod to Twight and Extreme Alpinism).
Thinner baselayers made with faster wicking fabrics and construction (as discussed previously) best fit and indeed demand action layers that prioritize breathability. For example, take the opposite extreme, a 200 grams/meter 100% merino shirt which was “cutting edge” 15 years ago. Hike uphill hard with a pack, even around freezing, and the shirt will get quiet to very wet. Pop above treeline and get hit by wind, or turn the crest and head downhill with the associated drop in heat production, and you’ll want something to moderate evaporation, least you get cold. Traditional windbreakers work well here, with limited breathability (<5 cfm, say) making for something of a wetsuit effect. The disadvantage is of course that further measures will be needed to get ahead of the moisture curve, and if kinder ambient conditions don’t help you out, external heat of some kind, in the form of a fire or added insulation, will eventually be needed. Modern layering seeks to avoid this, with systems that retain far less moisture under adverse conditions, and need far less input to dry.
There is a broad range of functionality here, with individual metabolism providing heavy influence. Smaller folks, leaner folks, and those with slower metabolism often need a vastly warmer and more protective action layer. For every case their is emphatically such a thing as too little or too breathable protection. A case of too little protection would be the aforementioned thick merino and windbreaker combo, which in most cases has too little insulative value and too much protection against external forces, which makes the body work to hard to maintain equilibrium, which is in turn a poor use of calories and morale. Too much protection would be a thin synthetic t-shirt and a 100 weight fleece pullover in the same conditions. This combo is good at moving moisture, statically warm, but provides little protection against external conditions (e.g. wind). This past fall I revisited using 100 weight fleece in place of a windshirt, and it only took one brisk day and one cold and still morning to think that the lack of control with respect to the wind and transpiration generally was stressing my metabolism more than seemed necessary.
This is why the nylon 20D mechanical stretch nylon Patagonia developed for the Nano Air series, a fabric found on its own in the Airshed pullover, might be the most significant development in outdoor apparel in the last decade. The insulation used in the Nano Air Light (above) is different that Polartec Alpha, but the reason it and the regular Nano Air are utterly different in use than other active insulation I’ve used is the shell and liner fabrics. Not only are they very (but not excessively!) breathable, but the thin, mechanical stretch (spandex free!) fabrics retain amazingly little moisture. A few weeks ago I was out in -15F on consecutive days. On one the least breathable component in my system was my BD Alpine Start hoody, with a couple hours work putting a fine coating of frost against the inside. On the other, a Nano Air over a baselayer (the LaSportiva Troposphere) stayed dry after three hours of hard trailbreaking. The Nano Airs are even more versatile companions for people who run cold. Since getting one in late October M has hardly taken hers off.
There are times when a windshirt which blocks a lot of wind has no substitute, including (at least for me) a hardshell. The sadly discontinued Rab Windveil continues to be my all time favorite here, due mainly to fit and features but also to toughness. The Alpine Start also remains a favorite, and oddly the windshirt I use most but the one I might let go first. The fit is frustrating, as is the way it hangs on to just a little too much moisture when conditions are truly challenging. On the other hand it’s durable, balanced with respect to weatherproofing, and looks good.
If I had to pick only two items from all the action layers I’ve had or have, they would be the Windveil and Nano Air Light. The Alpine Start would be hard to give up, and the Airshed hasn’t been in my closet long enough for permanent consideration. The fourth item would be Haglofs Pile hoody, not because it’s more performance oriented than something like a Nano Air hoody (or what the Tough Puff, which I’d love to try), but because fleece still beats active insulation on intangibles, if not on performance.
Actions layers are the other area, along with baselayers, where I think premium items can be worthwhile. The Nano Air series, along with the best modern wind layers, are astonishingly efficient. The premium is steep, when comparing for instance a $35 fleece shirt and the $250 Nano Air Light, but just with baselayers when you’re wearing it almost year round, action layers are a good place to put dollars.
Bedrock & Paradox 
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