A NEW PARADIGM FOR ANALYZING PWPB SYSTEMS LIKE THE COLUMBIA OUTDRY EX FEATHERWEI
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Stumphges,
You said, “What is the outer hydrophobic layer made from? Do you have a sense how long the Featherweight might remain hydrophobic in the face of abrasion from brush?”
Under my microscope, the outer hydrophobic layer appears to have polycarbonate crystals embedded in its surface to provide the armoring function. My guess is that the armoring will still be there when the garment is eventually discarded as a result of liner delamination after too many wash/dry cycles.
You said, “Any other hypotheses to explain the decline of my Dynamo?”
If it is the same 12 denier material; then a drying temp higher that 140F, cumulative abrasion, or wash/dry cycles breaking fibers after ~4 years of use, could explain it. I suspect a combination of abrasion and wash/dry cycles more than excess dryer heat. The dryer lint screen holds the broken and discarded fibers after a drying cycle. Each broken fiber will increase the CFM and decrease the HH some amount. The only windshirt that I have constantly exposed to abrasion, while monitoring its CFM and HH once per year, is a 70 denier WT 1.0 Epic coated military windshirt. I do not know how a 12 denier fabric changes its HH and CFM each year from various factors.
The Fall 2017 Montbell UL Stretch Wind Parka, the model they are still shipping as of today, is cut on the bias to provide stretch. The material has no coatings, that impact HH or CFM, and can wear off. The following micrographs are aligned with the bottom hem to clearly show the bias cut.
20mm FOV
5mm FOV
1.4 mm FOV
We have no way of knowing the exact HH and CFM or your jacket from the 2014 time it was manufactured. What we need to focus on is what is the HH and CFM of it now. You own a 2015 Houdini which I tested at 3.7 CFM and 387 mm HH, when new. Lets compare them now. For the CFM, my DIY coffe filter test is explained Here and my DIY HH test is explained Here
You should be able to assess the current relative CFMs (easy) and absolute CFMs (harder) of your two windshirts and the MB should be higher. The HH of two cups of water that is squeezed, at the pressure that will normally break a fully-inflated-cheap-party-balloon, is ~1200 mm. if you just pour in 2 cups of water and don’t squeeze, the water will quickly leak out at less than 100 mm. At 300-400 mm, not squeezing the fabric will result in a few drips but it would take more than an hour for the 2 cups of water to drain out. The relative pressure for each garment’s squeeze test will tell you if they are both still >300. If the MB leaks at about the same pressure as the Houdini, it is still a viable >300 mm HH active-rain-gear item. If not, it is still an excellent windshirt for moderate aerobic output <7 MET if still at 17 CFM or an optimal 3 season backpacking windshirt for 7 MET if it is now as high as you previously estimated.
1. No; it is a long chain polymer, that doesn’t get applied to just the ephemeral surface like all conventional DWRs except Epic. It is permanently bonded into every fiber and fiber void of thin 2D item’s (fabric). It uses different chemicals, a high-pressure plate (~360 PSI), and heat to permanently bond the individual fibers and voids with a cross-linked polymer. There is also a second hyperbaric chamber application process for 3D items.
2. Pertex Shield versions described on the European Montane Website:
I just measured a Pertex Shield + garment and it has 0 air permeability By US convention, PU coatings, with 0 air permeability, are not called microporous; they are called monolithic. This is explained in the second paragraph of my PWPB prologue via the embedded link. From the above, it is obvious that this convention is not followed in Europe and hence, the confusion… sorry. The applicable REI page segment is shown below:
Woubeir,
Alan Dixon wrote the Entrant G2 XT description, you referenced, in 2/4/04 (more than 14 years ago). He described it as a “micro-porous membrane” which to a US audience meant that it was air permeable. His Figure 1 (DPMC test results) clarified that:
Microporous membranes and coatings do not change their MVTR based on the average RH. In contrast, monolithic membranes and coatings do. This also applys to bi-component membranes and coatings that have a monolithic component.
Relative to your second question, the plate pressure reference is in paragraph 14 of the GTI US patent application. The patent application doesn’t provide the specific PSI they use for each scenario, it provides broad coverage by stating that it is a “superatmospheric pressure in contact with the fibrous substrate”. One scenario, I am aware of, used 363 PSI as the upper bound.
Adam Kilpatrick said, “The new Montbell windshirts are out. Different US and Japan market versions; fabrics seem the same but with the usual smaller sizes in Japan windshirts with slightly different features. The Tachyon in the Japan market seems to have no zips, and is called something different.
Montbell are claiming higher water resistance and higher breathability than their previous versions. Both versions (hooded, non hood) seem to have non-zip pit vents as well which is different to the past (my Japan market Tachyon bought 2013 in Japan has no pockets or pit zips). Be interesting to see how they fair.”
Per Adams request, I tested the new Spring 2018 Tachyon Parka as a potential Active Rainwear Garment (ARG), in the Hot Red color. It is a 7 denier Ballistic Airlight Rips-top nylon windshirt. It has two zippered hand pockets, an internal stuff pocket, and 3 gill vents under each armpit. The size I tested was XL and it weighed 2.845 oz. The CFM was 20.2 and the HH was 176 mm. Ideally, we want ≥300 mm for an ARG; so, I can’t recommend it for that function.
Versus the ARG recommended Montbell UL Stretch Wind Parka’s 17.6 CFM / 422 mm, the CFMs were similar but the HHs were quite different. The problem is caused by the lack of a uniform weave spacing. The following 2 micrographs are both 5mm FOV; the red material is the MB Tachyon Parka and the blue material is the MB UL Stretch Wind Parka. In the micrograph of the red fabric, note the larger pores at the corner of each woven square pattern. That is what caused the relatively low HH. I say relatively, because 176 mm HH is significantly better than the 70 mm HH of the popular bench-mark pre-2013 Houdini.
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