- Jul 9, 2019 at 2:23 pm #3601258
It is widely believed and asserted that DWR coatings are essential to the function of waterproof breathable (WPB) clothing, because once the outer fabric face of such clothing becomes saturated, or “wets out,” moisture vapor transport rate (MVTR) from inside to outside more or less stops. I’ve only seen one authoritative source dispute the widely-held assumption, and it was BPL’s own Ryan Jordan, here, wherein he asserts:
<p style=”padding-left: 40px;”>Contrary to popular belief, a layer of water on the outside face of a fabric doesn’t “dramatically” inhibit the transport of water vapor molecules through a WPB membrane. Rescue swimmers wearing WPB dry suits who spend long times submerged in the water report that during periods of high activity, they sweat, and in periods of low activity, they dry out. Makes sense – you’re not pushing water drops through the WPB membrane, you’re driving molecules. Wetted out face fabrics are problematic for body heat loss, because the “wetter” (more water) in your clothing, the more body heat is lost to drive the evaporation of that water.</p>
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Is anyone aware of any information, evidence, primary sources that support Ryan’s claim?Jul 9, 2019 at 3:57 pm #3601268
My personal experience, not speculation, is that once the DWR (Durable Water Repellent) treatments fail, due to wear or poor quality, WPB (waterproof breathable) garments do not work, and I get wet, either from condensation and/or water penetration.
Of course there are many types of WPB barriers, and my experience does not apply to all of them. It does apply to Goretex, in its iterations of 5-10 years ago, to H2O-NO WPB garments from Patagonia from that period, and to several cheap and flimsy so-called ‘2.5’ products that went into the trash. The Patagonia garments (Specter pullover, M10 jacket) with care have lasted at least 10 years, and the M10 is still going strong. The latest products are over-hyped, and I do not have the ability or desire to experiment with them, and no need to, with the M10 still workig fine.
I do not wash my raingear, as it is used only in downpours in cool to freezing weather, and there is no need to. Did wash and hot-dry a Specter in Atsko that was used in Hawaii and returned with sweat stains on the inside, and carry it on dayhikes; but have not had to use it, so don’t know how the DWR was affected. I do know, again from experience not speculation, that any type of spray containing silicone will often destroy WPB barriers and water will penetrate. Tectron DWR aerosol sprays, rated tops in the heyday of Backpacker mag, did not contain silicone; but a few years ago they put out a pump spray that does. Ouch!
Since the advent of WPB, most of the stuff I’ve tried has been poor quality, over-hyped, and not fit for its intended purpose. So these days I stick to a couple brands I trust, Patagonia and Montbell. Also understand that Arcteryx is OK but expensive. From being a regular reader of the BPL forums, I get the impression that the SUL (Super Ultra-light Weight) craze has led to the purchase of a lot of junky WPB products. No surprise, living in the age of fake everything.Jul 12, 2019 at 9:52 pm #3601665
Paul McLaughlinBPL Member
It’s very hard to come up with any hard and fast rules when it comes to moisture vapor transmission through a garment in actual use. There are theoretical scenarios galore, and anecdotal experiences covering just as wide a spectrum. So of course it is possible for a laminate to transmit moisture vapor despite a completely wetted out exterior, if the planets align. The physics simply require a gradient in terms of temperature, humidity, or both in order for water molecules to move one way or the other. But it will be harder to achieve that with a wetted out fabric because in that scenario you can only have a temperature differential, you obviously don’t have a humidity gradient when you are going from the inside humidity to a saturated outer layer. Yes, of course there can be evaporation from the film of water on the outside of the fabric, but that is a separate event. So the wetting out of the face fabric does not make moisture transfer impossible, but it does make it less effective.
Of course all of this is clutching at straws, since the real challenge is that almost all WP/B fabrics have such a low MVTR that you have to play a very close game of temperature control to to have any chance of making them work. You must keep your moisture production (perspiration) down to the minimum while keeping the temperature differential between inside and outside the garment as high as possible. If you get any warmer than just barely warm enough you are usually over the line. My own experience is that i have to be either sitting still, or I have to be working in cold weather with minimal layers on. As in, shell and baselayer at 40 degrees. And I can’t go up a steep hill at my usual pace and expect things to keep working, I have to slow down or I’ll overheat and start to perspire. to put it another way, I have never found a fabric that is waterproof that breathes well enough to allow me to go uphill at my usual pace without significant condensation.Jul 13, 2019 at 5:10 am #3601712
STEPHEN SBPL Member
If we assume 80 oF skin temp and 90% humidity inside the suit and 50 oF water temp and 100% humidity, the vapor pressure across the suit is .277 psi. This should be adequate to make moisture travel across the membrane. However, is this enough to dry it out, as the OP suggests will occur? I guess that depends. As stated by Paul, these membranes always have limited ability to move moisture. In general, at a high level of effort you can add far more moisture than can cross the membrane. As I suspect we all know, even during cold winter conditions, when exterior vapor pressure is very low and vapor pressure across the membrane is very high, we can still entrap lots of moisture in layers beneath our WBP outer layer with a high enough level of activity. I think claims of getting wet and then drying out should contain a little more discussion about the circumstances.Jul 16, 2019 at 5:05 am #3602115
Paul, re: ” I have never found a fabric that is waterproof that breathes well enough to allow me to go uphill at my usual pace without significant condensation.”
So, I slow down, which makes sense when the treadway is being soaked by rain. But had this discussion on another thread, and Daryl & Daryl reminded me that some perspire much more profusely. So for you guys, I guess that Richard Nisley’s long thread about alternatives to WPBs is helpful.
As for the OP’s question, could someone explain how moisture vapor can pass through a GTX laminate with a fabric outer layer, when the fabric’s DWR (durable water repellent) treatment has worn out, and the fabric is soaked through by rain? Would like to know.Jul 16, 2019 at 9:48 pm #3602179
First, you have to understand the basic premise that the outdoor industry is one of the few large industries (industry numbers suggest that in 2016, the outdoor industry generated approximately $887 billion in consumer spending and provided over 7.6 million American jobs) which has no ‘governing body’ and therefore no performance standards of any kind for any product which have to be adhered to. Hence anyone can say or print whatever they wish to make their products look good or in most cases, better than the competition. Fortunately, there is a good deal of product integrity from most brands for the simple reason most of them realize that in some situations, lives may depend on their products. The other side of the coin is the consumer in general is lazy when it comes to taking care of their gear and more importantly, understanding how their gear really works, which in turn creates unrealistic expectations of what a product can or should do in a wide variety of weather conditions. This, coupled with a lot of well meaning but misinformed opinions based on personal experiences/expectations instead of scientific facts, has created the confusion you refer to, especially when it comes to DWR, breathability, waterproofness, etc. This is simply my personal opinion based on over 40 years of working in the outdoor industry, five years as an Outward Bound instructor in NC & CO and eight years as a pro ski patroller at a major Colorado ski area, not to mention countless personal trips and adventures.
DWR is a heat flowable polymer which is designed to create surface tension on the fibers of the face fabric in order prevent liquid moisture (rain, snow, etc.) from being absorbed into the fibers – think tiny ‘fingers’ holding a droplet of water above the surface of the fiber. It has everything to do with the comfort of the wearer and absolutely nothing to do with ‘waterproofness’ or resistance to water entry pressure. The loss of a DWR finish is typically caused by abrasion by shoulder straps or ‘masking’ of the DWR finish by dust or smoke from a campfire. Once the finish is gone in a specific area of a garment, liquid water is absorbed into the fibers which creates the ‘wet out’ effect to which you refer. ‘Wet out’ has minimal effect on reducing breathability (more on this later…) but it can create discomfort and in some cases cause the person wearing the garment to think it is leaking. The ‘leaking’ effect is caused by the difference between wet conductive heat loss and dry conductive heat loss, i.e., wet conductive heat loss is up to 23 times faster than dry conductive heat loss or simply, a wet t-shirt vs a dry t-shirt on a cloudy, cool day. The good news is the DWR finish can be restored by washing the garment and putting it in a dryer – be sure to follow the manufacturer’s care instructions. Since the DWR chemistry is based on a heat flowable polymer, the heat and dwell time of the dryer will in most cases restore the finish. If it doesn’t, then use one of the restorative products on the market (take your pick…). Washing is also critically important in that it removes the dust, smoke particulates and other ‘impurities’ which affect DWR performance. One thing to keep in mind is the DWR chemistry itself is changing rapidly due to EPA mandates based on environmental concerns. In the last five or so years, it has gone from a C8 chemistry to a C6 chemistry and is in the process of moving to PFC free chemistry. All of these transitions are great moves for the environment and need to be done… however, for the outdoor consumer, DWR performance will continue to decline, no matter whose garment we are talking about.
Most people think air permeability and breathability are the same and while a garment which is air permeable is certainly ‘breathable’, the same cannot be said for garments which are breathable but not air permeable. Think of ‘air permeable’ as air (wind) going from the outside in while ‘breathable’ refers to the transfer of moisture vapor from the skin from the inside out. It should also be noted each is measured differently, i.e, ‘air permeability’ is measured in cubic feet per minute (CFM) and ‘breathability’ is measured in a variety of test methods, the two most common being Moisture Vapor Transfer Rate (MVTR) and the Sweating Hot Plate (Ret or Resistance to Evaporative Transfer). Part of the issue in understanding breathability is the confusion around test methods – remember the part about ‘no industry standards’?
MVTR numbers are pointless and essentially worthless when used to correlate human subjects and real world conditions which in turn really means their only real value is that the large numbers they tend to produce can make a great marketing story. The first problem is there are at least ten different MVTR tests, e.g., upright cup, inverted cup, etc., so which one correlates best to breathability of a fabric under real field conditions? Answer: none of them. Essentially, MVTR tests are used for quality control in the manufacturing process and are performed under strict lab conditions (temperature, humidity, wind, etc.) and in accordance to ISO and ASTM tests protocol. The value of the test is to ensure a product meets predetermined performance standards from batch to batch.
The Sweating Hot Plate on the other hand correlates directly to actual field conditions because it measures ‘resistance to evaporative transfer’ (Ret) of a specific fabric. The Ret of a fabric does not change even if environmental conditions (temperature, humidity, wind, etc.) do and equally important, the measurements are cumulative. For instance, if you are wearing a base layer, a lightweight fleece and a WP/B shell, each has an established Ret number (lower is better) which can then be added together to establish how much resistance there is to the transfer of moisture vapor from the skin (also known as ‘breathability’). Obviously, having multiple layers between your skin and the WP/B shell creates a lot of ‘resistance to evaporative transfer’ but just for fun, we prefer to blame our ‘expensive WP/B garment’ for our lack of understanding and resulting discomfort. FYI… the Sweating Hot Plate and Ret measurements are the generally accepted test method for breathability by the leading physiological labs in the world (Natick Labs, Hohenstein Institute, Kansas State University, etc.).
The other misunderstood part of breathability is the concept a ‘driving force’ between your skin and the outer layer of fabric, which simply means that in order for any breathable garment, be it a WP/B shell or a wicking base layer, to ‘breathe’, i.e., transfer moisture vapor from the skin to the outside of the outer layer of fabric, it has to be cooler and less humid on the outside than on the inside. So if you are in a hot, humid environment like the AT in the summer, then you have no chance of any garment actually being able to function properly in these conditions. Yet, somehow we expect our ‘expensive WP/B garment’ to be an A/C, climate controlled wonder of engineering. On the other hand, if you are skiing in the middle of a 30 degree F powder day and are layered properly, your ‘expensive WP/B garment’ should function as it is designed.
As far as ‘wet out’ DWR impeding breathability, essentially if there is enough driving force between the inside and outside, then the moisture vapor from your skin will be ‘driven’ through the ‘barrier’ and absorbed into the liquid water. Think about how WP/B waders work underwater… there’s nothing more ‘wet out’ than standing waist deep in a cold mountain stream fly fishing…and I can tell you from personal experience that they breathe just fine.Jul 17, 2019 at 4:26 am #3602224
Dan, I’m not familiar with WPB waders, but am wondering if WPB function does not depend on an effective DWR treatment, then why do manufacturers provide a DWR treatment on rain wear, with better treatments provided on more expensive brands? And why do the better brands keep me dry inside, and the lesser ones not much?
Should note that most of my treks have been either in the spring or later summer, and in the northeastern or Rocky mountains, where it has been cooler. That is more to avoid bug seasons than anything else, because with limited vacation time, I want to enjoy trips as much as possible. But it could be another reason why, other than on day hikes, I’ve not experienced the summer heat and humidity on the AT to which you refer. Other possible reasons, such as different degrees of sweating or hiking speed experienced by different people, were also brought up in this thread.Jul 17, 2019 at 4:52 pm #3602286
Google ‘SIMMS Fishing Products’, one of the leading fly fishing brands and you can find out more about WP/B waders… SIMMS introduced the first WP/B wader using GORE-TEX fabric in the mid-90’s so the concept of breathability underwater is well vetted by thousands of guides and hard core users. Though these waders have a DWR finish, it is similar to what is applied to garments – again, DWR is applied for comfort, i.e., to prevent ‘wet out’ and does not affect water entry pressure (waterproofness).
In my experience, better brands do not necessarily use better DWR – most of it is the same chemistry, especially with the change over to PFC free chemicals. The difference is usually found in the ‘WP/B technology’ which in turn equates to the best combination waterproofness and breathability which is typically found in the more expensive brands. Generally speaking, a WP/B jacket that retails for $99 will not have the performance attributes of a jacket that cost $400. Yes, WP/B technologies can vary greatly from brand to brand but in my experience the time tested wisdom of ‘you get what you pay for’ generally rings true, with the caveat that nothing works perfectly in all conditions. In fact, I find an umbrella works best in some conditions…
The one thing to remember is ‘comfort’ is not an absolute value, but rather one which is perceived individually, i.e., if you take a group of people and give them the same clothing system, they use it under the same environmental conditions and perform the same activity, there will be a variety of ‘opinions’ as to what is ‘comfortable’ – some people will be too hot, some too cold and some just right.Jul 17, 2019 at 10:23 pm #3602362
Generally speaking, a WP/B jacket that retails for $99 will not have the performance attributes of a jacket that cost $400.
Although the two of them may have been made in the same factory in China at a wholesale cost of about $30 each. Ah, but the extra marketing spin has to be paid for.
CheersJul 19, 2019 at 5:36 am #3602554
Your second post filled in my blanks, and made a convincing statement. Thank you. Should we conclude then that the DWR is not key to the performance of WPB rain wear; but that the ability of the fabric to repel water and prevent saturation of the outer fabric improves comfort in cooler weather by increasing heat retention? Most of my hiking is in open, unprotected areas, at higher altitudes; so greater protection from chilling alone is enough for me to stick with DWR treatments that do a good job of repelling water.
While chilling in the rain is more of an issue in the Rockies, I recall a hike at much lower altitudes on the Maine AT in the summer when a co-ed college outing club stayed either in front of, or behind me for several days in the rain. Besides filling up the shelters like clowns in a VW, (which they were keen on), a number of them developed hypothermia and things looked worrisome. Fortunately, the sun eventually came out, and all was well.Jul 19, 2019 at 7:12 am #3602556
Should we conclude then that the DWR is not key to the performance of WPB rain wear
It is not that simple imho!
First of all, as you probably know, I dispute the whole WP/B concept as a bit of a marketing fraud. If something is genuinely waterproof, it will NOT be breathable for air. It may permit some water vapour transmission, but that is rarely enough to keep you dry inside. I will not use the term WP/B myself.
If you are taking about a membrane-based fabric, then I would argue that the DWR is in fact crucial to the performance of the fabric in transmitting moisture. If the surface wets out, you lose 99% of the transmission of water vapour immediately, because the water layer on the outside is now blocking any movement of water vapour, and never mind the membrane. You will note the huge importance Gore place on having an active DWR on the surface of their fabrics – for very good reason.
CheersJul 19, 2019 at 4:56 pm #3602588
Much can be said (and has been said…) about the performance or the lack thereof of DWR, waterproofness, breathability, etc. When all is said and done, the primary objective of rainwear is to keep you dry. Comfort is a secondary objective and highly dependent on one’s personal perception of how well a product meets their expectations, realistic or not. Yes, DWR is a critical element in the wearer’s perception of comfort but has no effect on water entry pressure (waterproofness) and very minimally on breathability. There are far too many interacting variables such as your level of fitness, age, gender, constantly changing environmental conditions, level of exertion, layering, driving force, etc., that are much more critical to your perception of comfort than the condition of the DWR finish. Each of us is responsible for our own safety and comfort when it comes to the enjoyment of the outdoors, which to me is far more important than arguing about the performance (or not) of DWR, WP/B garments, etc.
Roger… having worked for Gore for almost 30 years (and now retired), I respectfully disagree with your comments on DWR and WP/B products. Obviously, we both have different experiences and understanding of how this concept works or not. My final comment is I know which product I will be wearing when the weather turns ugly.Jul 19, 2019 at 9:35 pm #3602613
Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
A lot of criticism on this site for WPB with DWR
My experience is it works pretty good.
Totally waterproof gets wet from sweat, terrible.
Poncho flaps around in wind, I’d rather have a jacket with arms.
WPB with DWR will get wet if I’m exercising vigorously. Or maybe if it rains hard for extended period. But it will dry out after a while when conditions improve. It’s the best compromise.
If it’s going to get wet I’ll just wear a base layer. Okay, maybe it will get wet at some point, especially on back and shoulders but it’ll dry out when conditions improve.
I try to wear as little as possible and slow down to minimize sweating. I look at weather reports and try to avoid periods with lots of rain. An oversized jacket is good so there’s room underneath for ventilation. I’ll unzip the front if rain isn’t blowing in to maximize venting.Jul 19, 2019 at 9:52 pm #3602617
the primary objective of rainwear is to keep you dry.
I disagree. To my mind, what really matters is staying warm enough for survival. If I am canyoning in a wet suit, I will be wet all over, but that does not matter as long as I am warm enough. To be sure, if I am just standing around in the street, getting wet will not be good, but actively walking is a different matter.
It depends on the situation, doesn’t it?
DWR is a critical element in the wearer’s perception of comfort but has no effect on water entry pressure (waterproofness) and very minimally on breathability.
I agree that DWR has no effect on the hydrostatic head rating: that was never at issue. But I do claim it affects breathability very significantly, which is why Gore place so much importance on maintaining and reviving the DWR on their fabrics. A continuous film of water does not have a very high breathability, does it?
Poncho flaps around in wind, I’d rather have a jacket with arms.
That depends on the poncho, doesn’t it?
Neither my Mountain Poncho nor the Packa flap around in the wind, and both have sleeves.
Neither design goes between your back and your pack, so both allow your body to breathe. You don’t end up with a wet back.
Poncho design has advanced from the basic Gatewood cape era.
CheersJul 20, 2019 at 12:29 am #3602636
Bruce TolleyBPL Member
@btolleyLocale: San Francisco Bay Area
“A continuous film of water does not have a very high breathability, does it?”
LOL!Jul 20, 2019 at 3:58 am #3602658
STEPHEN SBPL Member
“A continuous film of water does not have a very high breathability, does it?”
In the context of a WPB membrane it may. JIS 1099B is one of the commonly used breathability standards and is capable of producing really large breathability numbers. One side of the WPB is actually submerged for this test. If you look at the example I posted above, you will see the vapor pressure differential whereby a WPB membrane can transfer moisture across a membrane where there is high, even 100% humidity on each side. In this case, it takes a temperature difference, not a humidity difference to provide adequate vapor pressure differential to move vapor across the WPB membrane. However, if the exterior surface is dry, rather than at high humidity due to wet out, it will move more vapor, all else being equal. None of this means that the WPB can move enough vapor under any circumstances to remove all the moisture you can generate at high activity levels. All garments tend to involve trade-offs between thermo-regulation and other objectives. The user must make the right choices to maximize his choice of garments for a specific activity and activity level. There are no magic clothes (yet) that can do this for you.Jul 20, 2019 at 4:56 am #3602661
Sigh. Comes of me trying to simplify things.
OK, let’s consider a real case. I am walking along a high ridge in cold wind and rain. The outside of my jacket is wet because the DWR has failed/gone. How much water vapour will the jacket now ‘breathe’?
The problem here is more complex than it seems. First of all, I am continuously generating sweat or moisture even if the amount is small or ‘insensible’. We all know about this. Next, that moisture is diffusing outwards through my clothing layers, however many they may be, until it hits the inner surface of the jacket. To pass through that ‘WP/B’ fabric layer will require either a humidity gradient or a temperature gradient (or both).
Given that the outer surface is saturated (the DWR has been lost, remember), the only humidity gradient is likely to be in the wrong direction: inwards, not outwards. To be generous we will accept that there is actually zero humidity gradient.
So I will need a temperature gradient to push water vapour out. BUT, there is a cold wind and rain outside, so the outer wet surface of the fabric is subject to wind-chill and is cold. What will the inner surface be like? Given the very thin nature of the so-called WP/B fabric compared to any base-layer clothing I am wearing, we can very confidently say the inner surface is also going to be cold: not much more than a degree or two above the outer surface. If there was any more sustained temperature gradient you would be losing heat so fast you would soon collapse from hypothermia. The inner surface of the fabric is also likely to be at least damp from condensation.
So now, in our real-world case, we have no humidity gradient and precious little thermal gradient across the fabric. Just how much water vapour transfer through the fabric will we see? My answer, based on the laws of physics rather than marketing spin, is ‘very close to zero’.
There is a secondary problem with a membrane fabric like GTX. If the DWR rubs off or gets dirty, by going through scrub or across a rock face for instance, then all that is left is the membrane barrier. If the membrane barrier is damaged by sharp spikes or holly leaves or anything similar, the membrane will also leak. I found I was getting wet around the shoulders in my expensive GTX jacket, so I had it tested by Gore themselves (here in Australia). When water pressure was applied across the fabric, there was a veritable shower-head of jets of water spraying out. The membrane had been spiked many many times, and my expensive GTX jacket was now useless in the rain.
If you are a TV reporter standing still interviewing someone in the rain, or a traffic cop standing in the middle of some cross-roads in the rain, a GTX jacket is probably a very nice thing to have. No argument. But those conditions do not describe our needs.
EDIT: I have ignored the possibility of a pressure gradient. Since I don’t go around looking like a Michelin Man, that seems reasonable.
Jul 20, 2019 at 6:19 am #3602664
- This reply was modified 4 months ago by Roger Caffin.
Eric BBPL Member
“DWR is a heat flowable polymer which is designed to create surface tension on the fibers of the face fabric”
Not necessarily. Many DWR treatments are not polymers at all, much less “heat flowable”, whatever that means.
Examples: PFOS, PFHxS, PFBS, among many others.
Jul 20, 2019 at 6:34 am #3602666
- This reply was modified 4 months ago by Eric B. Reason: typo
There seems to be a fair amount of disagreement expressed here in response to the OP’s query, to which I replied:
“My personal experience, not speculation, is that once the DWR (Durable Water Repellent) treatments fail, due to wear or poor quality, WPB (waterproof breathable) garments do not work, and I get wet, either from condensation and/or water penetration.” I said “and/or,” because don’t know for sure once the DWR wears out, and the top wets out, how much of the moisture is from condensation, or water penetration, or both. As a practical matter, it doesn’t make much difference – soaked is soaked.
Others’ experience may be quite different. Went back and re-read Alan Dixon’s excellent BPL article on WPB materials, and it did not provide much in the way of answers. There are just too many variables in personal metabolism and climate to know in advance what will work, if at all. But bottom line, agree with those who believe that if one is going to use a WPB raiin top, the DWR needs to be sufficient to keep the garment from wetting out. A two week rainy trek in northern Colorado wilderness in a “2.5” WPB pullover that immediately wet out hammered that lesson home. Surprise! – LL Bean made a full refund.
If WPB doesn’t work, there are alternatives, like Roger’s Mountain Poncho, the Packa, Paramo, cagoules, and other gear that will not keep you bone dry, but reasonably comfortable in rain storms, (with some fleece insulation underneath if needed).Jul 20, 2019 at 7:08 am #3602667
When we did the GR5 in France (8 weeks walking), we had several weeks of intermittently bad weather. Some days were ‘kinda wet’.
Our silnylon ponchos worked just fine, in wind, rain and snow.
Later this day we reached the Brevent teleferique going down to Chamonix. It was a bit late in the day and we were resigned to walking all the way down. Fortunately the operators had not actually shut the lift down yet, so they grabbed us when we wandered in, stuffed us into a telecabine (hustle, hustle), and pressed the Go button. We emerged at the bottom in Chamonix wondering how we were meant to pay for the ride. Realisation slowly dawned that the operators had actually wanted us ‘off the mountain’, and were not worried about the fare. Very nice of them. It was ‘sort-of’ fine in the valley.
CheersJul 20, 2019 at 9:21 am #3602669
Sean PBPL Member
@wily_quixoteLocale: S.E. Australia
So, a WPB jacket can transfer moisture across its membrane except when wetted out and at low temperature when the driving forces fail. Then it becomes as bad, or perhaps imperceptibly better, than a impermeable barrier (I.e silnylon) in terms of ‘breathability’ but no less waterproof.
so, I still don’t see the advantage in a silnylon jacket as it never performs better, in terms of breathability, than a wpb jacket and in less extreme conditions performs much worse.
clearly a garment designed to ventilate better (a poncho or variant) made of silnylon might be better performing than a jacket made of either a wpb or silnylon but it seems to me that a poncho made of a wpb would outperform a poncho made from silnylon or any jacket as it would have both properties of ventilation and vapour transfer.
This is an argument about garment design, really, and to which degree ventilation under the garment affects performance.
i suspect that for a hiker encountering conditions where a poncho has less utility, for example off track walking in scrubby terrrain, this argument is pointless as it still must be decided whether a wpb membrane in jackets has any utility. It does, clearly, just not a lot when the DWR is gone and/or wetting out is sustained.
The degree in which a walker can expect to be exposed to a wet out jacket and consistent rain would determine the fabric type. I still don’t see an advantage in silnylon as it cannot perform any better – just sometimes is equally as bad as a wet out wpb jacket. In all cases optimising ventilation in a jacket should be an effective strategy.
of course if a silnylon jacket is cheaper or lighter, and you are seeing continual rain, that choice might be better. Or a poncho of any kind might be better if terrain suits it.Jul 20, 2019 at 9:25 am #3602670
Sean PBPL Member
@wily_quixoteLocale: S.E. Australia
Jul 20, 2019 at 10:14 am #3602672
- This reply was modified 4 months ago by Sean P.
seems to me that a poncho made of a wpb would outperform a poncho made from silnylon or any jacket as it would have both properties of ventilation and vapour transfer.
Great theory, but it does not seem to work that way in practice.
A major advantage of a silnylon poncho over a ‘breathable’ one is that it is lighter, less expensive, more waterproof, and packs smaller.
I get plenty of ventilation in my poncho when I need it.
Scrub: yeah, of course we wear our ponchos in scrub when it is cold and wet. Wet silnylon fabric really slides well over wet scrub.
Jul 20, 2019 at 11:20 am #3602679
- This reply was modified 4 months ago by Roger Caffin.
Geoff CaplanBPL Member
@geoffcaplanLocale: Dartmoor, Devon
Is there any hiking scenario where you would take a conventional jacket rather than your mountain poncho? For example, a route like the Sierra High Route that involves a bit of scrambling?Jul 20, 2019 at 1:54 pm #3602691
Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
if there’s a film of water on the outside
perspiration could go through the fabric and then condense on the film of water
the film of water is cold which would produce condensation
but this is just physics
I hike all over in pacific northwest and use WPB/DWR. I do some bushwacking, but not through thorns or whatever that would poke through the fabric
I have to hose off the outside occasionally to get the dust off it. I noticed the last time I wore jacket in rain I got a little more wet than seemed reasonable – maybe I’ll wash it with a treatment to restore the DWR. Not a big deal though because underneath jacket I have a thin nylon shirt which tolerates getting wet.
I use 2.5 layer WPB. After a few years the membrane will delaminate. That’s the price of having a lightweight WPB. I put a liner on the shoulders and hood which maybe doubles the lifetime.
I have a 30 year old 3 layer Goretex jacket. I’ve used that backpacking and other. It’s still water resistant. It’s rather heavy though. It has lots of REI features that add weight.
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