"Finally, rain jackets aren't just for rain. Many of us live in drier climates where we don't see much rain. We carry them just in case. But we also carry them to trap heat in the morning/evenings or to provide additional warmth in our sleep systems. Having a fabric that breaths well in those situations is also very attractive."



A windshirt would be just as good, if not better, in those circumstances.

Thanks for the detailed report. It verifies a similar conclusion I had come to after years of wearing Paclite and switching to an eVent jacket last year. I could definitely feel almost a cooling effect inside the eVent piece.

The point about darker colors changing performance deserves more attention at retail.

'Finally, rain jackets aren't just for rain. Many of us live in drier climates where we don't see much rain. We carry them just in case. But we also carry them to trap heat in the morning/evenings or to provide additional warmth in our sleep systems. Having a fabric that breaths well in those situations is also very attractive.'

"A windshirt would be just as good, if not better, in those circumstances."

I've sat on that teeter-totter so many times with clothing selection (or gear selection in general). If I were going to take the absolute minimum number of garments, a rain shell trumps a windshirt for handling harsher conditions. It is an easier choice if the forecast is for rain-- the windshirt can stay home. The real quandary is whether you should march off into the backcountry with no rain shell if the weather is good. IMHO, that is where a DriDucks jacket comes into play.

Of course what everyone wants is a 4oz rain shell that breathes like a windshirt. {up music, Jimmy Cricket singing "Wish Upon a Star."}

I was simply replying to Warrens post, Dale.
Due to the unpredictability of the Scottish weather, i always carry a rain shell. I always carry a wind shell too. As Chris posted earlier, being damp in Scotland is usually a fact of life. Staying comfortably damp is the ideal.
I try to wear my rain shell as little as possible, and the windshell is worn on nearly every trek i'm on.
The only time i leave the windshell at home, is if i'm wearing Paramo in winter. My Aspira smock goes on at the start of the day, and stays on.

im sure not too many people here are fans of mister gryllls

there was however this one episode where they simulated hard windblown rain and bear did his best to survive it overnight under a tree branch shelter ... they used a heat camera to record his temps ... he was wearing no rain gear, just DWR and standard outdoor clothes

he basically went hypothermic in short order

now you may think hes a showman or "fake" ... but theres no denying that he is a very fit and mentally strong person, more so than the majority on this site

if theres only one shell later i NEED to bring ... its a waterproof

"im sure not too many people here are fans of mister gryllls"

Jeez, Eric, that is like going to the Cable Guy for computer support ;) I value your experience and opinion far more than the PT Barnum of Survival!

If you want to get wet and cold, the west coast of Canada is a good place to start, seconded by my climate 100 miles south. Rain gear is mandatory. I have allowed myself to take a DriDucks UL poncho when going on day hikes on August; the rest of the time, I'm ready for a deluge-- or 24 hours of drizzle and wet brush.

Thanks for all the hard work on the testing.

Finally, rain jackets aren't just for rain.
Absolutely. Usually when I'm wearing rain gear it's NOT raining hard. I too am usually wearing it for a wind shell, for warmth, or even while doing laundry on a long hike. A good breathable will do these jobs as well as serving as rain gear.

...it is inevitable that sweat will condense on the inside of the shell (which is cooled by the outside ambient temp). Some mistakenly think this condensation comes from rain leaking in." I agree.

I also agree that it's important to accept certain discomforts that are unavoidable, like a certain amount of wetness when it's really rainy, but the gear we use and how we use it can make a big difference.

When the DWR treatment wets out the WPB membrane doesn't breathe as well so condensation build-up inside is greater. But the WPB membrane remains waterproof."

I agree.

Mark referenced this article: High Exertion Moisture Accumulation in Rain and Wind Shells

In that test the breathable shell resulted in 6 oz. of sweat in the base layer, and non-breathable, 10 oz. I consider that to be significant difference in comfort. Since this forum is all about lightweight backpacking, carrying an extra 4 oz. of sweat, and presumably 4 more oz of water to replace that sweat, is worth considering.

Another thing to think about.
Like many on here, i don't carry spare clothing (apart from an insulating layer), and sleep in what i am wearing. I include my clothing as part of my sleeping system. If i allow myself to get more than damp, i could be in for a cold night.
I realise that this probably sounds stupid to folk who hike in dry climates.

Finally fully updated the comments I posted earlier. I went on a bit eh!?

Conversation does seem always to go back to what is best practice... and everyone reverts to their anecdotes. As I'd suggested before, I'd like to see more hard data being gathered to give us a better idea of what's going on.

The question that vexes me the most regards the wideish range of temperatures recorded inside the jackets. Is that purely caused by lower breathability putting greater heat-stress on Will, or do some of the jackets naturally have higher internal convection, radiative heat transfer, etc. (in the ways I suggested in my previous comments), or are other factors at work I've missed out?

Without improved understanding of what's going on fabrics and membranes might get better but product design isn't.

Chris Townsend wrote: "When the DWR treatment wets out the WPB membrane doesn't breathe as well so condensation build-up inside is greater. But the WPB membrane remains waterproof."

Unfortunately this is false. It is a long-standing claim that originated with Gore and is just marketing, not fact. It has been repeated by so many people so many times that it has become an article of faith, but it just ain't true.

When a WPB fabric wets out due to failed DWR, water *will* leak through the membrane. And it gets worse as the fabric gets folded/bent/worn with time. (It's possible that brand spanking new fabric straight from the factory wouldn't do this but that's hardly relevant to the real world.) I've seen this happen with several different jackets and have tested it myself.

I'd love to see Richard or one of the others here with hydrostatic head test equipment demonstrate this.

Stuart, I'd like to here more about the science behind WPB membranes working in reverse.

Reason being, I've certainly gotten quite damp inside my WPB shell during all-day rain. Problem is, it's rather impossible to judge the source.

In September of 2009 I arrived in the little resort of Stehekin Washington. Having just hiked through three straight days of rain through Glacier peak wilderness on the PCT.
I had never been this wet in my life. All my gear, clothes, spare socks, everything was sopping wet.
I was embarassed and felt I had somehow "failed" even though I had used all the outdoor skills of 18 years of hiking as well as the past 5 months spent walking from Mexico.
It was hilarious when i met up with a large group of fellow PCT hikers and discovered that every single person, despite what they had for rain gear; ponchos, expensive WPB jackets, cheap dri ducks.. every one of us was completely soaked to the bone.
The more seasoned long distance hikers simply used a wind shirt and umbrella.
No, they don't stay dry either. The windshirt gets wet and the umbrella slows the replacement of that warm moisture (warmed by body heat) with the cold rain thats falling.
For sitting around camp the high techery works great.
For hiking all day, everyday, through the rain expect to get wet.
There is a saying among long distance hikers:
The only cure for three days of rain is a motel room.
I am not alone in coming to the conclusion that a simple 99 cent plastic poncho is as effective as any 300 dollar WPB jacket at keeping a person dry or rather less wet during multi day rain.

I don't think that the membrane is leaking. What is happening is that the wetness is body sweat and condensation when the DWR fails. At least this has been my experience.

I don't believe that the total saturation of the outer layer of a WP/B shell (or other item) leads to a reverse passage of water from the outside to the inside. For example, I have several single-walled WP/B tents (from Bibler, ID, and Nemo), and they certainly don't leak through the fabric even when the outside is entirely wetted-out (rain water no longer beads). And what about fishing waders that are constantly immersed in water? They don't leak through the fabric, and are undeniably more comfortable to wear than non-breathable, but waterproof, alternatives.

@David,

I've only ever found one article that explained this in great detail and had lab test to show it, but it was a print article from over 10 years ago. I haven't been able to locate it or any similar reports on the web.

It's interesting to try and find any lab tests that actually support Gore's claim that the wetness you get when the DWR fails in solely from perspiration and not from external water leaking through. I haven't been able to locate a single report that backs their claim. As far as I can tell the origin of the claim is Gore's marketing department.

I will have another look around the web to try and find some science to backup my statements.

I have tested it myself though. A goretex jacket with the DWR well and truly removed (it went through the washer twice with detergent...). I draped the jacket over a bucket and filled the depression with water. And couple of hours later, there was about half an inch of water in the bottom of the bucket. I'm pretty sure the bucket wasn't perspiring :) After a good wash-in DWR treatment, the same test produced no water in the bucket.

I've done this with two other jackets, one gore-tex (>10 years old, had never had its DWR renewed apparently) and the other some proprietary goretex-like membrane. Same results.

Anecdotally, I've had DWR-less goretex let heaps of water through the shoulders with me just standing in the (heavy) rain for a couple of hours - there was no sweating going on (yes, I know about insensible perspiration - it is insufficient to explain the amount of water that got through.)

I'm always surprised when people repeat Gore's claim about this. I just assumed everybody knew it was just spin.

Cheers

@Stuart - your experience certainly suggests that the fabric is leaking. I have had gortex paclite wet out under extreme (rain) duress, but I have not had it leak. I have also had internal condensation that could have been assumed to be leaking through except that the rain was cold and the internal moisture was very warm.

This definitely calls for some scientific analysis by BPL!

Consider that the membrane may simply be overwhelmed with perspiration as well as the shell wetting out and about the same time. The relative humidity is also increasing as the air is saturated after hours of rain--- everything is soaked inside and out and the whole system spirals into a soggy mess.

As Matt found out in Stehekin, after that many days of rain, the cold moist air has permeated everything-- the air, ground, foliage, your gear and clothing. And you're working hard, hauling your load in steep terrain. There is a real difference in moisture management with hours or days of cold drizzle in saturated landscape vs something like a thunderstorm in an otherwise dry environment.

Could someone explain how a wpb membrane like goretex could "reverse" and let water in?

I am a bit skeptical, as I have used goretex and goretex knock off dry suits and paddle pants while immersed in water and didn't notice any leakage. It would seem if the only thing preventing the wpb membrane from reversing is the dnr coating then I should get wet, yet I don't, as the coating is completely "wetted" out while underwater.

Is it possible that the folks are just noticing that when the surface of the fabric is wet it no longer allows moisture out? Or am I completely missing what people mean by the membrane "reversing".

It would seem like this would be an easy thing to test out..

Great article by the way.

Many thanks for the article and all the interesting comments. Excellent stuff.

I was intrigued by the GoreTex over a bucket test. It's interesting to note that during a hydrostatic head test the outer fabric is saturated yet results can be >20000mmH2O. But here we are talking about leaking over longer time frames.
Could it be that the water from the puddle on top of the membrane is evaporating through the membrane and condensing on the lining? I say this on the basis that condensation occurs not just because of the dew point conditions (temperature, humidity and pressure) but because of the water repellency (surface energy) of the material. The hydrophylic PU layer may have this effect but a scrim lining with washed out DWR would play a similar role.
In the case of waders there's a temperature gradient that may be counteracting this effect and the time scales are different, too.
It's important to realise that water attaches to hydrophobic surfaces, unless they are superhydrophobic, like a lotus leaf (Cassie-Baxter conditions), and that small forces such as gravity or even subtle shaking (of the floor?) may allow droplets to spread out, possibly allowing water to creap through pores in a membrane. This situation can be seen in the lab when droplets on a hydrophobic surface slowly spread out over time.
Alternatively, a simpler explanation may be that the membranes were damaged, physically or by chemical contamination, in all the tests carried out.

Quite right!
I add this comment because it seems to be pertinent to breathability in the rain:
Some people contend that when ambient humidity is 100% no breathability occurs. On the face of it that's true, except where you can warm the air enough for it to absorb some moisture and then wisk it away on a breeze; or in the down wind part of your clothing system where the aerodynamics create a low pressure zone, allowing the air to absorb more moisture than the ambient conditions. So wind and heat loss seem to me to be the key ingredients. But, of course, it's so much easier to get wet than to dry off, and harder to dry in high humidity conditions.
But getting wet's not going to kill you, it's staying warm that's important (thinking: mmmmm, hot bath). By the way, the Blizzard Reflexcell kit provides insulation that is far less effected by water than conventional garments.