Thanks for the hard work you've put into this, but I have to second Roman Vazhnov on picking up a number of minor issues that need consideration and add a few other points/corrections. I'll try to make this as brief as possible....
Roman rightly points out the importance of where the humidity sensor is placed in relation to zip openings. I used to own an Arc’teryx Alpha SV jacket, which proved to be useless protection from the cold in anything stronger than a breeze as its storm-flap-less pit-zips offered no resistance to wind penetration (but hey, great ‘breathability!’) On the opposite side of the coin, a big problem with zips is the amount of extra seam-tape they require which locally prevent moisture transfer out of the garment - if the jacket is closer fitting, this effect will be worsened as there isn’t as much air movement inside the jacket.
Roman points to other sets of factors to take into account - aspects of the fabric performance (aside from the membrane) and garment fit make a big difference to breathability and insulation. (Why, you may ask should we separate fabric performance from membrane performance? Well all the branded membranes are offered to brands with a range of different face fabrics, and sometimes different linings too. More on this a little later…) Anyway, here are my points about fabrics:
Firstly, garment fit coupled with fabric stiffness and weight has a noticeable effect. Stiff baggy shells (e.g. shells with laminated fleece linings) hold much of their surface away from the wearer, and with static folds of excess fabric, trap spaces of still air inside the garment - effective insulation. (This is partly why stiff heavy shells are popular in the sailing fraternity.) Of course more insulation = more heat stress = more sweating = humidity. It’d be very difficult to measure this effect, but it’d be interesting to hear if Will thinks this might have been a factor with any of the test pieces.
Still relating to fit, the second factor is garment coverage – how low is the hem and high is the collar? More coverage = more insulation and more area where sweating’s evapourative-heat-loss is hindered = more heat stress = etc. (you know the equation!)
Thirdly, the insulating effects of a shell may go further. If a shell is closer to equalising its temperature with outside cold it will promote more condensation on its lining which will reduce our humidity measurements (though not necessarily improve comfort over the long-run – which depends on what then happens to the condensation – my next point.) It’d be interesting to see the R-values (insulation) of the different text piece fabrics. (I really don’t know how much variation there would be and nor do I know how far this might affect condensation – can anyone enlighten me?)
Fourthly, if higher air-permeability allows wind to rapidly cool the jacket’s internal microclimate, then condensation and attendant higher conductivity and evaporation chill will occur deeper inside a layering system (if midlayers are worn - not in this test) as the dew point moves inwards. (Note that venting after building up a sweat will also have the same effect – so it’s best venting before you get all hot and sweaty in the first place!) This is only mitigated by the fact that as the jacket is so breathable, less humidity will have built up inside it in the first place. Of course this point is part of the common objection to air-permeable waterproofing – it’s not entirely windproof.
My fifth point is how shell linings aid comfort in a way not measured by this test – a good lining will absorb condensation or otherwise make it more acceptable (why 2.5L isn’t as comfortable as 3L). Maybe Chris Townsend’s experience with Neo and Active shells having less condensation than eVent is that they are faster at absorbing and spreading out condensation than the rather run-of-the-mill light grey tricot that lines eVent fabrics?
This brings me on to the sixth and final point. Point #4 in the article doesn't emphasise that any particular membrane will be laminated and sold with a wide range of different face fabrics all with their own varying levels of performance - it's not that one fabric is always mated to another membrane. I’ve seen suppliers’ own lab-test results and the same membrane will have vastly different MVT scores when laminated to different faces (sadly I’m not at liberty to quote figures). To sum it up, there is little consistency for the consumer to rely on and no marketing that one can take at face value - what's new?!
An aside… midlayers and insulated shell technologies can hinder moisture transfer in your layering system far more than the shells that might be worn on top of them. My Mtn Hardwear ‘monkeyman’ jacket is a bad offender. With ‘high-loft’ surfaces on inside and out, it is densest in the middle so capillary action doesn’t work in its favour. It seems to be particularly good at just holding moisture and getting claggy (unless I wear it exposed directly to the wind, in which event I may as well not wear it at all). Other bad offenders are synthetic fibre insulated garments (Primaloft etc) - two windproof layers with a thick still layer entrapped in a hydrophobic mat - all is not good on the moisture transfer front. Warm though! (I’d be curious to see how quilting shell and/or lining to Primaloft might vary breathability - a wind-flapped shell layer could help convect moist air through the otherwise inert fibre mat.)
Finally those (slighly anal) corrections I promised:
As Roman pointed out, GoreTex membranes generally aren’t air permeable (Their tent membranes are and perhaps Active Shell is too?!)
“A plain woven fabric without any membrane or coatings can be very breathable... but not water-resistant” - I dispute that. A dense weave/non-woven fibre mat + DWR, or Ventile can be highly water resistant.
“A polyurethane membrane requires two phase changes (vapor to liquid to vapor) to vent moisture” - true for hydrophilic PU membranes (and also that famous polyester-polyether block copolymer membrane- Sympatex), but there are also hydrophobic microporous PU membranes too. These act much like ePTFE. I suspect Neoshell is one of these and as I’ve hinted above, Gore’s Active shell maybe a combination of ePTFE + microporous PU, as opposed to their usual ePTFE + hydrophobic PU lamination, but I might be wrong?
There... I'm done! :)