By the Numbers: The New Breathability Gap in WPB Jackets and What the Breathability Tests Get Wrong

My neoshell jacket never wets out.  In extreme conditions it will start to wet out, …

I find this conflicting info; or it wets out, or it doesn’t. Unless you mean wetting out is only when the complete jacket is wetted out, just not simply several patches.

@Ryan: read WO 2016/029922 (filed 2014)

Yeah, my neoshell, maybe it will wet out in patches, but not enough that water accumulates inside surface of jacket.

no,  I never had that too in a 3-layer jacket, but in my Paclite I did and certainly the sleeves.

I think it is safe to assume C0 coatings aren’t oleophobic.
Reasonable to assume this currently, but it depends on the chemistry (although the promising ones are still at the lab stage).

…

At least, unlike we thought in 2015, we know now that C0-DWR can be oleophobic

Actually, this needs some clarification:

C0 (fluorine-free) DWR is hydrophobic but not oleophobic — and it cannot be, by surface-energy
physics. The core problem: fluorine-free surface energies (hydrocarbons, silicones ~20–25 mN/m) sit at or above oil surface tensions (20–32 mN/m), so oil cannot be repelled by surface energy alone. Three workaround mechanisms are being pursued: liquid-like dynamic surfaces, re-entrant textures that trap air, and ionic self-assembly. Fluorine-free oleophobicity is now proven in the lab (e.g. grafted PDMS “liquid-like” brushes, hierarchical reentrantstructures) but none is commercially mature; grafted PDMS is the leading candidate.

(based on a conversation with Mistral Vibe AI)

Regarding the change I showed from the old Pro to the current Pro. The 2017 Beta AR that I tested had a Pro fabric with a 40D shell.  The 2026 Alpha SL has a 20D shell.   FYI: The two Arcteryx Alpha SL Pro and the Beta SL that I tested for this article are shown below. I do not have an image of the 2017 Beta AR Pro.

 

Beta SL Pro

 

Alpha SL.  (image at twice the magnification as the Beta SL image)

You can see that in the two ePE fabrics, a Tricot knit backer is used.  It is unclear whether the Microgrid backer is used with ePE.

actually, that’s a circular knit, not a warp knit. So C-knit, not tricot

Woubeir: You are right.

All academic studies on the impact of rain or wet-out on MVTR are old and use older fabrics whose performance may not be comparable to today’s membranes.  Also, some test methodologies raise questions that cannot be answered. I am going to build a kettle that can go in the shower.  There are a number of issues to figure out, but I think it will be feasible; time will tell.

would you do things like seeing if the DWR wets out after several hours of rain?

@Stephen: are you sure the red picture is from an Alpha SL? Because Gore itself says that ePE Pro uses only the Micro Grid Backer

https://www.gore-tex.com/technology/gore-tex-products/pro

Woubeir: I looked at the link you provided.  I don’t have the jacket here, but, I checked my invoice and it was Alpha SL.  I cannot explain the discrepency.

Jerry: That is the plan.  Of course, it won’t be rain, it will be a shower.  Wet-out is not the main focus, but if or when it occurs, its influence will be measured.  I probably won’t have anything to report until December, or later.

Just from experience in the field, wetting out seems to be the most important factor.  In the circumstances I’m in – temp, amount of rain, exertion level,…

Looking forward to any results.

Jerry: That is the plan.  Of course, it won’t be rain, it will be a shower.  Wet-out is not the main focus, but if or when it occurs, its influence will be measured.  I probably won’t have anything to report until December, or later.

My quick trials in the shower have been, shall we say, not very helpful. I think that a shower’s potential volume & pressure are more intense than “normal” rainfall.

A sprinkler setup may be more “scientific” where the rain is allowed to fall via. gravity, somewhat separated from any excess pressure/velocity that is possible very near a shower head. A simply rain-gage could be used to “calibrate” the test.

I say all that speaking moreso of “testing” the wetting-out of exterior face-fabric layers. If you have other testing-goals, then this of course might be worthless commentary.

Admittedly, one of the other issues with testing “wet-out time” has to do with the jackets DWR condition, before one even starts the test. Meaning, how long did that jacket sit on the shelf, before coming to you? Was it still sealed in the plastic protective wrap, as it sat undisturbed on a warehouse shelf, or did it spent months on a retail hanger getting “used”? Was the jacket washed & dried before use, as some brands recommend, but not all it seems?

I wish it were simple, but as many things in life prove, lots of variables to consider… :/

For me, the most important issue would be: a jacket has a certain MVTR when tested in a dry condition. What happens to the MVTR when the the fabric is wetted out? How quick is not important to me. If I’m on e.g. a 10-day trip, it is not important if it’s after 10 minutes, 1 hour or 2 days. I just want the same performance on the last day as on the first day.

Woubeir:  I don’t know about that.  One academic study I read supported your point.  Another concluded that rain hitting and running down a fabric produced similar temperature and humidity impacts as wet-out. So, we will have to keep an open mind.  How these tests are configured, and how they affect the thermal conditions on both sides of the shell, will influence the outcomes.   Also: on the Alpha SL. In my invoices, Arcteryx includes a photo of the product. The colors match my images.  On their product description, all they say is Nylon backer.  I would conclude that there is a disconnect between the actual product and what you read in the link you sent.

Read this article about WPB degradation.  I find it disturbing, but it does not seem to agree with my experience.  I need to spend more time reading it. Download is slow, so be patient.

Well, actually, I want to be comfortable all the time (with the ultimate goal of maximising my comfort level at every instance during my activity (well, one can at least dream of that, can’t they?)).

So also on the moment that it is cold and rains constantly. If I have my rain shell, I am more or less as long as the face is dry, I’m definitely less or even not when the face is wetted out. I don’t know precisely which factors influence that, but the wetted out face is definitely one of them in that jacket.

Stephen, here’s a citation for the Marxmaier article AI told me about: Marxmeier, H. (1986). Chemiefasern/Textilindustrie, 36/88, July–August, p. 575.

Also, it is apparently at least partly summarized on page 311 of Holmes, D. A. (2000). “Waterproof Breathable Fabrics.” In A. R. Horrocks and S. C. Anand (eds.), Handbook of Technical Textiles. Woodhead Publishing, pp. 282–315.

Here’s a link to that handbook:  https://rexresearch1.com/TextilesLibrary/HandbookTechnicalTextilesHorrocks.pdf?utm_source=chatgpt.com

I hope all this is correct and helpful.  If so, I will gladly take credit.  If not, I didn’t do it – AI did.  ;- )

By the way, Stephen, you said you think Toray Torain is the microporous membrane to beat.  Why is that?  In the MVTR test, several others beat it (albeit not by much) or basically tied with it.

Hi Andrew, thanks for the book.  I have other books in that series.  I’ll need to look for relevant chapters.  Microporous PU membranes have been around for a long time. However, the Toray Torain membranes take MVTR for that general technology to a new level, not only for breathability but also for durability, with their PC/PU technology. Toray manufactures these jackets and they seem to do an excellent job.  It seems to me that they are enabling a new level of performance with whatever feature set the clothing industry wishes to incorporate.   The North Face has a small lead in MVTR but their jackets do not incorporate all the features I want in a jacket. Still, I am bringing my North Face Papsura on every hike. If my Tushar jacket had proper closures on the hood and cuffs,  that might be my jacket of choice.

So do I understand correctly that the you favor the Torain membranes because they are more durable than anything with similar or greater MVTR?

I’m looking forward to the rain test results!  No doubt we will learn many interesting things.

Regarding the test – and wetting out – a few thoughts and questions …

First, Stephen, if I understand correctly, your current test procedure maintains constant humidity on the internal side.  However, if some fabric’s MVTRs drop faster than others in the rain, then to really understand how their performance deteriorates in rain, the humidity on the internal side of such fabrics would need to be allowed to rise more and faster than with other fabrics.  Otherwise the test would probably still provide a correct ordinal comparison, but would not provide a correct cardinal (numerical) one.  (I think this is also true with dry testing, but allowing differing humidity rises in the wet testing alone at least would give a better idea of how performance changes from dry weather to wet weather.)

Second, would the test procedure still measure how much humidity is able to escape from the test source, as opposed to measuring humidity inside the fabric?  While that’s how it should be done to measure MVTR, I believe it would be even more interesting to measure how much moisture (vapor and liquid) ends up on the internal side of the test fabric (whether on the fabric or in the space on the internal side of it).  If some fabrics permit water to get through, that could have a much bigger effect than how much vapor emitted by the wearer can escape.

Third, I think we are all agreed that not wetting out is hugely important.  But I’m not convinced that’s because of the impact on MVTR.  Suppose one fabric loses all it’s MVTR.  Then it would have the same MVTR as a rubber raincoat.  But on a cold, rainy day, I’d much rather be in a rubber raincoat than a wetted out WPB that lost all it’s MVTR.  That’s because of heat loss.

It’s often said a wetted out WPB loses heat by convection.  I suspect that is only part of the story.  If one jumps into a cold, running stream, one loses heat fast, and it’s not due to convection.  It’s because liquid water can absorb heat a lot more quickly than a similar volume of air, and if it doesn’t sit perfectly still next to you, then instead of the eventual, partial compensation of having warm water next to you (losing heat to any colder water next to it), it is replaced by more cold water which continues absorbing water rapidly.

I think something like that happens when a jacket wets out.  The water adsorbed by the outer fabric becomes just a continuation of the water sitting on or running down the surface, and heat flows quite freely between all of that water.  And when that water drips off, it takes heat away.  Or alternately, as more rain hits your shoulder, the water that had already soaked into your shoulder fabric makes it’s way to your chest, the water that had soaked your chest fabric makes it’s way to your belly, etc., until water is dropping off the hem.  As this happens, while heat from inside the WPB makes the water soaked into the fabric warmer, and thus less quick to absorb more heat, that water is replaced by new, cold rain water which keeps the overall temperature of the water in the fabric low, so it keeps absorbing heat from inside the WPB rapidly, lowing the temperature inside the WPB.

If water is able to fill the pores, it’s probably worse.  Then any liquid water on the inside becomes just a continuation of the water on the outside, enabling heat to more quickly pass to the outside.

And if water is not only able to fill the pores, but to pass from the outside to the inside through them, then presumably that’s worst of all.  Both because it can affect the layer next to the WPB, displacing insulating air and even collapsing it, and because cold water inside the WPB can more quickly absorb water from the inside layer.  All else being equal, it would certainly be the wettest, as the test would show.

A big question, in my mind, is how a fabric that keeps water out of the pores compares in heat loss to one that does not, but does not admit water to the inside, an also to one that does admit water to the inside.  As well as to MHPU membranes, of course.

Hi Andrew: You can get a comprehensive description in the article, from the section describing my test. Quick answer: The kettle controls heat to maintain vapor pressure differential.  RH will vary in a fairly narrow band. However, I have created a concentration test, which uses different size water trays to achieve higher or lower humidity levels. This allows me to study the concentration response of MHPU membranes.  When I run this test, the humidity concentration will increase, as it does with rain, because rain falling onto a WPB cools the face fabric and raises the RH on the other side of the liner fabric. I expect I will do a dry test under normal conditions.  Then, I will run the wet test under temperature control so the temperature in the ambient below the membrane will be maintained where it ended the dry test.  This should ensure the temperature drop on the inner side of the membrane when 50F water is falling on the WPB.  How well this will work, and what I will have to do to achieve condensation inside the WPB, remains to be seen.

I am counting on no leaking occurring. I expect the microporous membranes will have the right combination of pore size and hydrophobicity that the membrane will not admit liquid water. I will be able to weigh the condensate accumulation on the inner after the test.  Can the pores flood? Maybe, and we should know if this is the case. MHPU is monolithic. It should not leak. Like microporous, in principle, vapor transiting a membrane can condense inside.  I think it is more likely that condensation that accumulates on the inner layer will prevent vapor from reaching the membrane.  We shall see.

You are referring to water transiting these membranes.  They should only be traversed by vapor.

All of these issues will be a lot easier to think about once the thing is up and running.

The real problem with this test is I cannot purchase a WPB for testing and return it when I am done.  I will be testing jackets I own.  I don’t own much MHPU.  This will be a time-consuming test, so I will learn what I can and let BPL readers know.

For those that still believe the marketing talk that the pores are big enough to pass water vapour, but not big enough to pass liquid water, this explanation:

The Two-Stage Failure Mechanism

1. Nylon Face Fabric Failure: The “Air Barrier” Collapses
In a clean state, the DWR-treated nylon fibers trap a layer of air between them (Cassie-Baxter wetting state), which forces water to bead up. When oil coats the nylon, it fills the micro-textures of the yarn. The surface becomes highly attractive to water.
Water spreads rapidly across the fabric, creating a continuous liquid layer that seals the face fabric and cuts off breathability.

2. MP Membrane Failure: Capillary Wetting (Leakage)
The MP membrane is structurally a micro-porous matrix composed of billions of interconnected nodes and fibrils. Under normal conditions, water cannot pass through these pores because the entry pressure required to force water into a hydrophobic (>90°) sub-micron pore is immense.
However, once low-surface-tension oils coat the fibrils of the MP-membrane, the water contact angle flips to a hydrophilic/wettable state (<90°). According to the Young-Laplace equation, this changes the capillary pressure from repulsive to attractive. Liquid water is now spontaneously sucked through the microscopic pores by capillary action, causing the membrane to leak even under low pressure.

is that why a WPB jacket fails?  And you wash it and it works again?

That happened to me recently