Art wrote: "depends on what you define as a mid layer.
I tend to use Patagonia Cap 3 as a mid layer.
If you call Cap 4 a mid layer, my Patagonia Nano Puff is lighter weight than my Cap 4 zip, and much warmer.
Nano Puff can serve as a mid layer or outer layer depending on the situation."
Good points, Art. Thanks!
I was thinking of wicking fabrics that provide more insulation than a base layer, but not fiber "puffy" layers like the NanoPuff, down , etc.
It does get to be a "heavy base layer or insulation" quandary. What I had in mind as a mid-layer was warm wicking layer to wear under a shell in cold wet conditions, bivouac, or sleep.
The insight on the weight of the Cap 4 vs. the Nano Puff is good stuff. Do you have the weights handy on the Cap 3,Cap 4, and Nano Puff?
I see the same issue with a Mont Bell Thermawrap, which is about the same weight as the Power Stretch.
What I've wrestled with is duplication of shells and thinner insulation layers. The Nano Puff and Thermawrap are great products, but if you use a wind shirt, you are hauling two items that incorporate an outer shell, plus one thin layer of insulation. If I were to wear something like a Cap 4 or Power Stretch plus my windshirt, I end up with some intermediate insulation, plus wind and light rain protection, plus the wicking and breathability of the synthetic mid-layer. There is also the versatility of the mid-layer plus wind shirt-- each can be worn alone or together. I agree it would have to be pretty cold to be moving uphill with much more than a base layer and shell on.
The question comes up for cold camp/bivouac use, where thicker vests or jackets can come into play, like down or Primaloft. The layering scheme I had in mind was a short sleeve silkweight base and a wind shirt, supplanted by a long sleeve mid-layer like the Power Stretch or Cap 4, plus a down or Primaloft layer.
This is a three season package. I might escape the mid-layer in July/August in the Pacific NW, but not much more than that.
This July 4th found me at 4500' with cold mist and light rain, cold air from snow fields a few hundred feet above, and temps below 50F at camp. Of course, there was no direct sun at all under these conditions--- literally sitting in a cold cloud. Under way, there was a steep climb and I went a good part of the way in just a base layer, adding a wind shirt when things leveled off or out of the timber-- the open slide areas having more wind and rain. I wasn't cold until stopped at my destination and I added a poly fill vest and rain shell. I found I needed just a bit more insulation to be comfortable and something like a wicking mid-layer would have been perfect. I guess something like a Primaloft jacket might have worked too. The jacket weight would be near equal to a mid layer and vest (about 19oz), but versatility fails again-- it's all or none with one monolithic layer.
Shoulder season hikes can often be in cloud cover and rain. In Spring there are camps where a lake is in a cirque with cold air falling from snow covered peaks all around, dropping the local temp below the forecast for the area. Typical conditions are 45-50F and with high humidity. With no direct sun, nothing dries out unless it is from your body heat or a camp fire. This is where down sucks and poly fill excels-- and a wicking mid layer comes into play.