Polartec Alpha was developed for the military, as an insulation which would form the core of a garment that would, as an insulator, better straddle the divide between static and dynamic warmth. Alpha does this by being more air-permeable than synthetic fill insulations such as Primaloft and Climashield, and at the same time more svelt (and thus better suited to shelled jackets) than fleece. Polartec says, “By placing patented low density fibers between air permeable woven layers we created a more efficient fabric for regulating warmth and transferring moisture.”
Warmth in the outdoors is often understood as an overly simple concept. Static warmth for a dry, stationary body requires only decent fueling and hydration and enough layers. Dynamic warmth, where said body is in various states of motion through varied environments, is governed by the same rules, but they are interrupted by the need to protect from external, while venting and moving internal, moisture. Achieving a balance between external protection and internal insulation is, most of the time, the key to sustainable activities in the outdoors.
Passable solutions to the various permutations of the moisture problem have no doubt existed for millennia. Pretty good ones have existed in the modern clothing paradigm for decades. What continues to be an occasional complication is finding a way to balance protection and insulation across a range of settings with minimal items of clothing, and with minimal alterations within the items carried. It is in this area where Alpha might make sense for some outdoor uses.
Alpha is not as warm for a given weight as the down and synthetic fill insulations to which we’ve become accustomed. The Rab Strata Hoodie weighs about a pound in size medium, 3-4 ounces heavier than the almost identically featured Rab Xenon X. The Xenon not only has a lighter weight (60 g/meter v. 80 for the Strata) of warmer Primaloft One insulation, it has a lightly lighter and far less air-permeable shell and liner fabric. One of the marketing saws for Alpha jackets, and the Toray-made clone used by Patagonia and Kuiu, is that the structure of the insulation does not demand the densely woven nylons which have become standard for Primaloft. This may or may not be the case, but I tend to believe that for an Alpha jacket to function coherently as a unit the liner and shell must do what they can to keep pace with the insulation. If Alpha can breath better and wick faster than the liner, moisture will stay stuck inside, against the wearer. If the liner and insulation can move moisture faster than the shell, or at least much faster, water vapor will become trapped inside, and in cold enough weather, freeze solid.
The Strata Hoodie does not do any of these things, and the liner (zoned mesh and light nylon ripstop) and shell (nylon plain weave with a textured inner face) seem ideally matched. The Strata moves moisture several times faster than the Xenon X.
This comes at a cost, and that cost is static warmth. The outdoor garment industry has taken a enhanced interest in breathability in recent years, one result being the many more, more air permeable garments available. Polartec Neoshell in the hardshell realm, woven windshirts like the Alpine Start, and Polartec Alpha are all examples. Breathability happens via moisture transport, and moisture within clothing systems happens via evaporation, which necessitates evaporative cooling. One of the reasons the Xenon and Xenon X jackets have made their reputation as the warmest garments of their class is the very air impermeable Pertex Quantum liner and shell. Summit a windy ridge after a sweaty climb and throw on the Xenon X and you’ll get immediate and considerable shelter from the wind.
The disadvantage is that the Quantum shells will also hold that sweat inside, and it will take time and often an external heat source of consequence to dry the jacket out completely. It is in these circumstances that I’ve become enamored with the Strata. It often provides enough extra warmth and wind resistance to serve as a resting or skiing-down jacket, while still moving moisture. The difference between how dry the Strata will keep me over the course of a day skinning and skiing laps compared with the Xenon is considerable. Similar things can be said when hiking slowly in moderate cold, or hard in serious cold. Worn over appropriate base and wind layers, these combinations are very effective, and impressively free from the need for constant adjustment.
The disadvantage of the Strata is in turn the lack of warmth, which is not due entirely to the increased air permeability. Patagonia hyped their Nano Air (which we can safely view as darn close in function to Alpha jackets, just with stretch), as the equal to Primaloft coats provided a very wind resistant shell (i.e. hardshell) was put over it when needed. My anecdotal experience is that this is not the case. 80 g/meter Alpha is significantly less warm than 60 g/meter Primaloft One, even when the two are compared strictly on terms of static warmth.
All this of course begs the question of whether the performance gains of the Strata could be united with a shell which is more wind resistant, or an insulation which is warmer. Would a partial mesh liner work with Climashield Apex, which is more robust than Primaloft and almost as warm? Would a chest and shoulder area with greater wind resistance significantly hamper the moisture transport of Alpha insulation? There are a number of such intriguing questions which might be answered by new garments in the next few years.
As a matter of backcountry policy, the Strata is often a very useful critter, but in most circumstances requires an additional insulating layer. What will best serve as a companion here, providing enough warmth without too much additional weight, bulk and complication, I have not yet decided. Fleece works well enough, but does not directly address the need for additional wind resistance, and insofar as both are bulky and suited to use on the go this combination is duplicative. Another, more traditional synthetic fill shell makes sense, but results in a heavy and bulky system. My hope, for spring hunting, hiking, and skiing, is to use a down vest in and outside the Strata. I will report back.