Current UL windshirts and breathability: are there other options and layering techniques?

The front panel of the Nine Trails is just like the Houdini. We did have some debate on whether the new Nine Trails uses the same fabric as the old Houdini or the new one. The Patagonia web site does show the same fabric as the older Houdini:

From http://www.patagonia.com/us/product/mens-nine-trails-jacket?p=25020-0 :
1.1-oz 15-denier 100% nylon, with 50-denier triple-ripstop yarns. Panels: 3.5-oz 75-denier stretch woven 91% all-recycled polyester/9% spandex.

For reference the current Houdini shows .2-oz 10-denier 100% nylon ripstop with a DWR (durable water repellent) finish (see http://www.patagonia.com/us/product/mens-houdini-jacket-windbreaker?p=24140-1)

The older Nine Trails was definitely the same as the older Houdini– I was able to compare them side by side.

Make sense?

Roman,
I would say it is very poor. Equivalent to one of those those super light (2-3oz) overly calendared nylon jackets like the Montbell Tachyon.

The Nine Trails is very minimalist. No hood and only one tiny pocket at the lower back that doubles as a stuff sack. Its a running jacket. Also no elastic hem cuffs at the wrist. I like the minimalist design for what I want it for.

The stretch panels are extremely air permeable, in comparison. You could easily make a mask out of this material and breath though it all day. I have no numbers, though.

Oh, forgot to say… I have not tested the DWR on it, but assume it is in keeping with other Patagonia products, which is to say it should be good.

And lastly, yes, I assume it is basically a hoodless hybrid Hoodini.

The Patagonia website is out of date. The Nine Trails jacket I just got sure seems like the identical fabric as the 2013 Houdini. It's the same by any measure, including the breath test. Not that it matters much since the entire back and sides of the jacket is permeable stretch fabric. I expect it to be a pretty good option for hiking. Weather resistance on the front, shoulders, and tops of arms. Very breathable elsewhere. 4.4 ounces.

No hood. But, in the summer when I'm wearing a ball cap anyway, that's not much of a problem. Even in the winter, I'm really liking the Capilene 4 beanie.

I never said 5CFM was a ceiling. We are currently testing several shirts, made specifically for backpacking, that are much higher CFM.

You are repeating a lot of conventional wisdom here. This community has advanced backpacking by challenging conventional wisdom. Respectfully, these bits of wisdom are worth challenging.

del

Michael

Perhaps you can recommend how i can use a low CFM windshirt in anything but a PNW winter

Currently with a very light long sleeve base layer and a windshirt (marmot trail wind) i sweat it out going between 30-40F and above

How do i make this low CFM windshirt work for me in continuous activities

Currently im reglated to using it for stop and go activities such as technical climbing, snowshoeing at lower temps, and as a very light weight belay wind jacket on summer rock

I cant use it for any streneous activities unless its decently below freezing

Hor do i turn this low CFM windshirt into something that is a bit more useful?

Also if i wear a fleece on top as you suggested (when it gets much colder of course), how do i prevent it from getting wet from the snow that will cling to it and melt with body heat? … PNW snow is particularly sticky as made famous by our skiing up here near whistler

And if i do wear that fleece above freezing (when moving slowly) how do i prevent the infamous PNW drizzle from soaking it through? … Or getting it wet from slush, condensation on the vegetation, etc … That a windshirt usually provides some protection against

I would really like to know the solutions are to the above

I already have a low CFM windshirt and woud really like to make it work for more than below freezing or stop and go activities

As to "challenging" wisdom … Every outdoor gear company claims they are, they all want to sell you a revolutionary concept or product

The reality is that most dont pan out very well

Once in a blue moon something will click though

Now if i can just find a way to not sweat in this low CFM winshirt even though im wearing basically nothing underneath

;)

All:

While the "layer over" technique I suggested was widely criticized, mostly by repeating conventional wisdom, I challenge you all to go do what Sala did, and try it. I honestly believe most of you will be pleasantly shocked.

Some asked me to explain what all this "layer over" hoo ha is about, so I will try:

First, just for discussion, let's remove rain and snow from the conversation, realizing we cannot remove it from the equation, since it is obviously a major factor. Also, let's forget about the term "wind shirt" for a minute, because that term in my opinion is half the problem. Instead of "wind shirt", lets call it a "second skin". But to let out the secret in advance as to why Sala (likely) did not get wet when he layered over, what we should really call it is a "semi-permeable vapor barrier". Finally, lets say that our goal is "to be as "consistently warm" as possible at the lightest possible weight hiking hard in cool temperatures."

First, we all know that you can put on a heavy 300 weight fleece, and if you hike and sweat you will still get cold in wind because of rapid evaporative cooling, in my climbing circle it was called "flash off". Your sweat evaporates too quickly and you get huge temperature fluctuations based on whether the wind is still or gusting. Very uncomfortable. But boy, does that fleece wick the sweat. You dry very quickly. Too quickly.

Now let's say that instead of that 300 weight fleece, we wear a "second skin" garment right above the wicking layer next to the skin. Even when it is cold, when you are hiking hard you are going to sweat, and in order to maintain consistent warmth, you need a way to consistently evaporate that sweat. A 2-5CFM second skin creates a humid, warm microclimate right next to your skin that eliminates "flash off" because at that low CFM the wind is mostly stopped. And because the air permeability is relatively low, even an extremely lightweight garment keeps you warm because it acts like a vapor barrier. It is the lightest way that I know of to stay consistently warm.

Now, I know that some have argued for a higher air permeability, and in some cases I agree, in fact SD is working on these exact garments for Spring 2015. But for now, let's skip that too and just stick with this 2-5CFM second skin…….

But of course this "second skin" it is not a vapor barrier, it is permeable, so the sweat does move through. When this is the only layer you are wearing, everything is fine. But now what happens when I am still cold? Respectfully, this is where most people blow it. "I have a fleece shirt, so I have to put it under my wind shirt" is the conventional wisdom. But this is not a wind shirt, this is a "second skin" a "semi-permeable vapor barrier". Do I put my fleece UNDER my semi-permiable vapor barrier? Of course not. That would simply expand the micrclimate and expose more layers to my soaking sweat. Now my sweat has to wick though my wicking layer, then through all that fleece, all the while getting colder and colder, minimizing effective evaporation, until I hit that wind layer again. Now with less heat and pressure to drive moisture through the wind shirt, water stays on the inside, soaking me, making me colder. But if I put that fleece on the OUTSIDE of the barrier, the second skin ACTUALLY WORKS BETTER THAN BEFORE, because now I have insulated my microclimate and allowed it to wick faster and more effectively. And as soon as that water passes the second skin, it can no longer cool me through evaporative cooling. (Your ridiculously over-priced 40,000 gmd2 MVTR GoreTex Jacket will actually move moisture too if you put it under your fleece, but I digress). The temperature and moisture in the microlimate are regulated, and the system works to keep me consistently warm, with the lightest possible weight. Think about the Intuit. Do they wear the Caribou parka with the soft fuzzy fur on the INSIDE? NO, animal fur gets progressively more air permeable the farther away from the skin (hide) it goes. Caribou evolved that way because it is consistently warmer.

Now, some have rightly suggested that the fleece, now on the outside, will not be as "warm" since the wind will cut through it more efficiently than when it is protected by the wind shirt. This of course is true, but even so, if you try it, you will realize that the wind has to be really blowing hard for this to overcome the benefits of the second skin, simply because it is managing your moisture way more effectively, dramatically more effectively. Just like I suspect Sala found. More importantly, who says that next layer needs to be a 60CFM fleece? It only needs to be higher CFM than the second skin in order to continue the evaporative process, and can still effectively block wind. The fact is you want some wind and airflow in that garment to dry the sweat that is coming thought the second skin, while that second skin blocks your microclimate from the effects of "flash off".

Finally, every time I post here I get bashed for being a corporate marketing liar scumbag loser. Before I take the inevitable beating yet again, let me just say that I think you are right that the big companies have failed you, and I agree that most don't give a crap about your puny little community, or about backpacking at all for that matter. But I do care, and so does my team. And I think you might find that if you give us a chance, our experience insight and passion for backpacking might actually add something positive to your conversation.

If any of you try this, and find that it is working for you, and find that you are believers in the second skin/layer over approach, I would love to hear about it and stay in touch. Because sometimes it rains (where I live it is more than sometimes) and everything above gets challenged by outside moisture. And if you really want to blow your mind and try something that challenges the status quo, have I got an idea for you…..

Rick:

I scrolled to find the post you were referring to, but couldn't. But from what you copied above I would say I agree with Eric Chans. The key is that "wind blocking puffy insulation" will work best if it is a higher CFM than the wind shirt underneath. Even if it is not, the concept still works, the puffy insulation will just gather moisture more than if it where higher CFM.

Too high, of course, and the wind will blow your heat out of that layer, reducing its effectiveness.

Eric Chan:

If you are too hot in your wind shirt, just take it off. If that is too cold, you need a higher CFM wind shirt. Jim Trombly, our Product Director, tells me that for most people the 2-5CFM works best because when it is too hot, you are not too cold without it. That is my experience as well. But you may find a higher CFM is what you need. To work properly, you should not be too cold when you take it off because you are too hot.

Also, are you sure that the Marmot Trail Wind is actually 2-5 CFM? I just did a quick check and could not verify. But at only $80, it is likely that the fabric was coated with PU in order to pass rainwear duty , and it could have 0 CFM as a result. If the garment does not pass rainwear (900mm water entry pressure I believe), it is subject to ridiculous duties, and the price goes up quickly. You can still get 2-5 CFM and pass rainwear (it is desirable in fact if you want to push it into light rain events) it is just harder and more expensive, and many brands focus on bitchin' color ways instead since most customers don't know or care about air permeability. It is like our MicroLight Jacket at Sierra Designs. Inexpensive, but totally useless for active pursuits. These jackets are best used for a lightweight travel piece that can block wind and rain in non-active situations.

Michael,

Thanks for taking the time to contribute with some fine detail. I think its pretty cool to have a professional gear designer such as yourself on these boards, so hopefully you can excuse the anti-corporate angst from a couple of us. I suspect that one reason for the resistance to your suggested CFM is that most of us have been going off of the CFM testing from our resident smart scientist guy, Richard Nisley. I'm not sure the reason for the disparity, but there's been a fairly consistent difference between his tested CFM ratings, and the ones listed by manufacturers. Some people have blamed the disparity on evil corporate lies, but customers don't know/don't care about CFM, so it would for poor marketing fluff anyway. My bet is there is a difference in methodology or machinery. Also, a few of the bigger advocates for the more breathable windshirts, including myself, are fast movers or like to do strange extracurricular activities like ski up mountains or go packraft-hunting (ahem, Dave C.) .

There's a dedicated thread to measuring different popular windshirts variables to help backpackers find a windshirt with a good balance of traits. Perhaps you'd be willing send Richard a stow windshirt for testing? I'd also be willing to get one out for some hikes around Boulder if you have any samples floating around. I've got a range of windshirts (I get one per sport right?!) with varying CFM including one made of pertex equilebrium that Richard tested at over 100 CFM, so I'd be curious to make a basic field comparison. I'd normally be BC skiing this time of year, but shoulder dislocation/surgery, has relegated me to cautious packless hiking.

edit: oh and here's the link to the thread mentioned above:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=87696

I have two windshirts, a home made one that use the original Momentum with a CFM of about 5 and a First Ascent one I got on super sale that is much more breathable. I have found that I am fine hiking in the Monentum one because it is mainly flat around here and I am not building up a huge amount of heat for the times I wear it. I think Richard agreed to something like this that 5 is fine if you are not doing strenuous activity.

I did try using my R2 fleece over the windshirt last week but can not remember what I thought about it so I will try it again today. Lately I have been wearing the windshirt over the fleece to get more of a Paramo effect when it rains or snows and that has worked pretty well but I am willing to try the other way.

What would happen if you did baselayer>5CFM windshirt>fleece>35+CFM windshirt? That way you could possibly build layers for when you stop.

Michael,
The most vocal do not necessarily represent the views of everyone. I for one, appreciate you being here because I value the insight behind the design process.

As an aside, I saw the DriDown Better Vest “t-shirt” at REI last night and I was very impressed. Comfortable, warm, and good fit. Looks like a great piece for a variety of uses. The reborn Sierra Designs is something I am very much looking forward to if you guys can keep up the playfulness and innovation.

> What would happen if you did baselayer>5CFM windshirt>fleece>35+CFM windshirt? That way you could possibly build layers for when you stop.

This is the system that Mr. Glavin suggests. I think it is a good one, although in my experience having a low CFM windshirt next-to-skin feels like wearing a VBL, although moisture does pass slowly. For UL backpacking needs, I would skip the high CFM windshirt and simply carry a puffy, since the low CFM windshirt and fleece will pass as an action suit. The only time a high CFM windshirt might truly add value in this alternate system is in blocking light moisture and snow, although I think most will find that body heat will serve nicely to push light moisture and snow to the very surface of the fleece, where it is of no concern.

It is a good system, one that works surprisingly well, but you do get a little damp — there’s no fleece next-to-skin to act as a large buffer. While you no longer get as comfortable a wicking action, you no longer suffer flash-off, which is the primary point of discomfort that a windshirt is meant to solve. I’ll need to experiment more in the coming weeks to consider the pros and cons of putting the windshirt inside instead of outside.

Fleece works very well for retaining heat except air flows through in sustained winds, so the windshirt adds that wind-resistance nicely, even when it is NTS. Think of it as similar to the membrane fleece jackets — half or more of the insulation is actually outside the wind-blocking membrane, but even in heavy blowing winds you never feel cold. The difference is that moisture wicks more readily through the windshirt.

Micheal

Thanks for your suggestion of taking off the windshirt … Unfortunately i would still like some protection from the snow, minor drizzle, and occasional wind gusts … So i a higher CFM windshirt/softshell would be the only way to increase the usuable temp range

You can breath through the trail wind just fairly poorly by puttin it to your mouth … Would that be 0 CFM? … There is some airflow

Im pretty sure its not 0 CFM

Now that youve explained it "removing snow etc" from the equation?

How do you propose exactly keeping snow drizzle etc off that fleece from getting it wet?

The reality is that when you wear that fleece over a windshirt theres a very good chance its in wintery conditions where theres snow or other fun moist stuff

What point is there in having fancy permanent DWR on your new windshirts if its not going to be your outer layer

I dont know about you but when i wear a very air pearmeable fleece on a windy day i really feel the heat loss … So wearing a windshirt or other less permeable piece will under will mean theres minimal heat loss from the insulation from the wind in the fleece? … Interesting

So its not tha you sweat less because the fleece is now less insulating now that its on the outside and exposed to the wind? … And thus less warm?

As to "corporate bashing" … Weve seen quite a few promises from companies here, many of them promising a new way of doing things, revolutionary products, etc …

Most dont pan out, rarely one does in a blue moon

Perhaps you can recommend the "best" layering system

Comventional wisdom for climbing consists of

Base (may include R1 based on conditions) -> windshirt/softshell -> synthetic light puffy -> belay jacket

Do you recommend putting the R1 on the outside of the windshirt/softshell? … If so how do you keep it dry from the elements

How does the SD layering system differ given 4 pieces(not including the emergency rain shell) … Base, (possily including R1), windshirt, light synthetic puffy, belay puffy jacket

As to the inuit … Dont their clothing have fur on the inside as well?

I always thought that they are much smarter than us folks for not over exerting themselves … Of course the early white men though them "lazy" for it

They know to sweat is to die … And varies their pace accordingly

Were the ones demanding high exertion activities innthe winter

;)

Edit to add ..

It was just in the last year or two that SD was promoting highly breathable windshirts that would "revolutionize"… Has everything changed this fast, or is the highly breathable windshirt low CFM?

Sierra Designs introduces innovative Cloud Layering System, redefines ultralight backcountry weather protection

Weighing in at a total of 22-ounces, this system is lighter than a bag of GORP and takes up less space in any pack. And while it may not taste as good as GORP, it will give much better weather protection.

http://www.sierradesigns.com/news.aspx?showarticle=371

Also in this article where you were quoted

“That’s bullsh*t,” says Glavin. “In reality, you are off or you are on, and there is no middle setting.” Backcountry travel has just two states of being, says Glavin: going and stopping. So “throw out that fleece/Goretex/layering crap and simply dress for the two situations you will encounter.”

http://www.bootprints.com/2013/4-steps-to-perfect-winter-layers/

How is this revolutionary compared to the "common wisdom" amoung climbers that have been preached by mr twight and kirkpatrick for the last two decades

http://www.andy-kirkpatrick.com/articles/view/the_art_of_not_suffering

http://www.andy-kirkpatrick.com/articles/view/the_belay_jacket

http://www.andy-kirkpatrick.com/articles/view/the_best_softshell_in_the_world

http://www.andy-kirkpatrick.com/articles/view/the_comfort_game

Way to stand up, Michael! Don't let the haters shout you down. Say your piece–we are listening! Interesting and novel concepts you put forward, all of it which can be determined empirically. I have to agree with you on two points:

(1) In the time I've been at BPL, I've found it heavy on cherished formulas, repeated wisdom, and groupthink. Whether you are right or wrong, I think injecting some non-conventional thinking is great. All you propose is testable. You've already given our community a lot of hypotheses to sort through. Thanks for the whack upside the head, if for nothing else.

(2) You are correct, there is a persistent, knee-jerk anti-corporate bias here. I for one find it offensive, in the same way I find racism offensive, because it makes negative, prejudicial assumptions about its targets, via insinuation, which may be entirely untrue. It takes balls for a representative of a manufacturer to post here more than once, to argue for his point of view. I like it! Keep it up, glad to have you on board.

Carry on…

A good discussion everyone.

All:

My apologies because I cannot find the methodology for measuring CFM that is being used to generate some of the numbers, though it is very likely that experiences are being judged on apples and oranges numbers.

We use ASTM D737 http://www.astm.org/Standards/D737.htm I asked Jim this AM and he tells me he is pretty sure this is the only widely used repeatable test methodology for air permeability. (note: this is different from MVTR, moisture vapor transfer rate, where there are many, and most use the higher-number-producting JIS standard vs. one of the more realistic ASTM methods)

A few other answers to some questions:

Q: It was just in the last year or two that SD was promoting highly breathable windshirts that would "revolutionize"… Has everything changed this fast, or is the highly breathable windshirt low CFM?
A: Nothing has changed, the cloud wind shirt is "low" CFM. In fact Trombly made us drop that shirt, though I really liked it, because the CFM was too low. 1.3CFM if my memory is accurate.

Q: Perhaps you can recommend the "best" layering system
A: I wish I could. I would say that the system I detail above would be "best", except that I non-realistically eliminated precipitation from the equation. I am an advocate for GO/STOP/RAIN, as detailed in the Cloud Layering System detailed above. In this system, you create the system that works best (described above), then cover it with a compromise rainshell in conditions where you will get wetter not wearing it than wearing it. Jim Trombly, our Product Director, has a view shared by most here that the GO system needs to have inherent water resistance, so it can be pushed into some more significant rain events. I think my way is simpler and more effective, particularly for beginners or lazy folks like me. Jim's is more of a "heady" performance solution. In any case, the "second skin" system is the best I have seen.

Q: How is this revolutionary compared to the "common wisdom" amoung climbers that have been preached by mr twight and kirkpatrick for the last two decades?
A: It's not. While I am not completely familiar with Kirkpatrick, the system I am suggesting is EXACTLY the one detailed by Twight. Its's only revolutionary for the 95% of people (albeit not 95% of those on this thread) are still using the "base layer, mid layer, shell layer" system.

Q: > What would happen if you did baselayer>5CFM windshirt>fleece>35+CFM windshirt? That way you could possibly build layers for when you stop.
A: In theory, the system will work better if each progressive layer has a lower CFM than the one before it. Any shift to a higher CFM layer will create a place for moisture to collect. But in practice, that system seems like it would work very well in a harder wind or light rain. Without those elements, my experience suggests you would be better off without the 35CFM layer.

Finally, since all we are (mostly) talking about is air permeability, it is worth noting that the "second skin" can be any CFM at all, and still work as a semi permeable vapor barrier. As the CFM goes up, so does rapid evaporative cooling in hard wind, but the cooler and drier the microclimate. It is just that at higher CFM, the term "wind shirt" begins to apply less. Air permeability is directly analogous to a measure of "windproofness". Most would agree, using ASTM testing methodologies, that a 35CFM layer could not be called windproof, and calling it a windshirt would surely draw the ire of those who dislike marketers.

"Q: > What would happen if you did baselayer>5CFM windshirt>fleece>35+CFM windshirt? That way you could possibly build layers for when you stop.
A: In theory, the system will work better if each progressive layer has a lower CFM than the one before it. Any shift to a higher CFM layer will create a place for moisture to collect."

Michael,
I seem to remember that in Twight's Extreme Alpinism, in the 'Action Suit' if you added a layer, that layer should be more breathable. However, if you add a 35 or so windlayer over a 250 or so fleece, that would not be the case. It would break the wind and remain thus the inherent insulative value of that fleece, but regarding vapor transfer it would be not so ideal I guess.

Breathable anoraks have been used in the arctic for millennia with layered wool garments. There were many made of uncoated nylon and were common for skiing and hunting in cold weather before Gore-Tex came into the fray. The 60/40 nylon/cotton fabric was another backpacking staple.

My use of a windshirt is along the same line and I want it to be very breathable. While water repellency is a plus, I do not want a waterproof barrier. I do want the lightest possible garment that will provide a breathable wind barrier, so I use a Houdini rather than the older style Supplex style cloth at three times the weight. Functionally it is the same.

In my layering system, I want my base layer to keep a warm DRY layer of air next to my skin and move my perspiration away to be transferred out through the windshirt. Any successive layers should also transfer moisture away from my base layer while remaining breathable. The windshirt will continue to act as a thermostat, slowing the loss of warm air near my body and protecting the warm layers under from convective heat loss from penetrating wind.

Putting a porous fleece over the top of a windshirt will add more insulation and it is quick and easy, but far from the most efficient.

Adding another shelled garment over a breathable windshirt is just like adding one over a button down shirt. Down proof fabrics are low CFM as well as the ones used for synthetic insulation, so you have three layers of fabric plus the lofted insulation for a stack of dead air layers. Acceptable for a rest stop, but not good for much of anything but sitting stil. Throwing a lofted garment on top of your other clothing is hardly revolutionary and quite conventional.

My preference is to choose a wicking base layer that suits the expected temperatures and add a breathable wind shell as needed. I also use fleecy wicking mid layers for additional layering under the wind shell for active cold weather or cool weather rest stops. That mid layer is also effective with my rain shell and as part of my sleep system. It is comfortable to wear around camp in cool conditions and can be worn while active on the trail without a wind shell, particularly while warming up from a cold start from camp or trailhead. It can also be worn while washing or drying my base layer.

I don't think thicker fleeces are weight/warmth effective and rely on synthetic lofted insulation for colder weather layering, still using the base and fleecy mid layers under. I could still use my windshirt in combination with a lofted vest but would leave it out of the mix with a full jacket unless it was very cold. I could use down garments in the same way.

I don't know how conventional that is, but it works quite well for me in the climate I usually hike in, with moderate temperatures, overcast skies with rain an deep forest cover.

As to anti-corporate attitude, I find it amazing that a Vice President would come into a forum of very experienced hikers and tell them that they are all wrong and that his new and revolutionary garments are the way to go. It's just a sales pitch. If I were interested in product development I would try to be more ears and less mouth.

As to Sierra Designs, I see their market position as an also ran with a succession of failing gimmick products. I would put their products somewhere between Red Ledge and Columbia.

1) The Trail Wind jacket is slightly more air permeable than a 2013 Houdini. It is not PU coated or water proof.

2) For Michael's windproof second skin approach, we are back to a Marmot DriClime windshirt as the base layer. Very thin wicking layer next to the skin to pass moisture to (and theoretically, through) the Pertex Quantum shell. I'll give that a whirl sometime. I guess the mechanism here is that the thin wicking layer will be damp, but there's so little of it, it won't be disgusting like a thick wet insulating layer. And, the moisture transfer out of the wind proof layer will be optimized.

Hey Dale:

I am sure sorry if I came off as saying "everyone is wrong"; in fact the reason I read these crazy threads is exactly because I am interested in learning from users here. Is my opinion less valid than anyone else's just because of my day job?

As for your assessment of Sierra Designs, I actually agree with you more than disagree. Working on it…….

I get that layering a fleece over a windshirt will keep the fleece dry because it's able to release moisture without being underneath a less breathable windshirt over it. I have a fleece hoody that I pull over my windshirt during breaks for convenience. However this only makes sense if it's not windy. If it's not windy, your wind shirt really isn't acting as a windshirt, it's an ultralight insulative shirt.
Layering over a puffy is different because puffy shell materials are typically wind resistant.

By the way Micheal, your kenosha jacket fabric is the most breathable windshirt fabric I've ever handled. I would wear mine more if it had a hood.

Hi Michael:

While I have used my (high CFM) windshirt in the exact way that you have suggested with very good results (ergo: "shirt"), I got hung up by something you said.

You said: "what we should really call it is a "semi-permeable vapor barrier"

In my profession (architectural), this is very confusing language to me. It is generally accepted in the building world that a "vapor barrier" (.1 perm or less) is never actually "semi-permeable", because it is simply a vapor barrier. Nowadays, a vapor barrier is commonly referred to as a "Class 1 vapor retarder"

I believe you probably mean "a semi-permeable vapor retarder", but this discussion about layering techniques has primarily been about the air permeability of various layers, not vapor permeability.

These two forms of vapor transport are not the same, in my opinion, and I believe that when we start talking about how to stay warm and not "overheat", the CFM measurement of a jacket is only part of the picture. (Even the word "overheat" can be considered misleading, since "overhumidify" may be equally relevant, and treated differently than overheating.)

I know there might be differing opinions about these definitions, and some may not care whatsoever, but in my 18 months on this list I have witnessed more confusion around vapor/air permeability than anything else. I think it might be due-in-part to people writing sharing their experiences using terms that all us readers interpret differently.
Perhaps its time we create our own "BPL list of snazzy terms" that we can all agree upon!

Although solely related to building science, here is a wonderful resource with many documents on the subject of vapor/air permeability:

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

For what it's worth, all this conversation about the "BEST" layering techniques reminds me of how to properly use manual transmission in a car. Once, I witnessed a conversation about what cars have the "best gear shift ratio", and answer that always seemed to show up was: "it depends on the road".

Matt

Good night man, y'all are some uber alpine athletes here or I'm just way out of touch these days. If I stumbled across this thread I would be under the impression this is a forum for self supported aerospace exploration. I understand the purpose in challenging conventions here, but how much performance do you expect from your windshirt? For f@%ks sake!

"Less gear, more beer!"

Great points, Matt. The term "semi permeable vapor barrier" was simply made up, by Mark Twight, I believe. And I am honestly unsure about the differences or similarities in the definitions of Vapor Barrier in construction and outdoor gear, the latter usually focused on completely impermeable barriers inside of boots or sleeping bags. But I will check out your article and try to educate myself. Heres a link to a useful article on the latter: http://andrewskurka.com/2011/vapor-barrier-liners-theory-application/

I agree there are all kinds of various terms that get thrown around without specific definitions. It sometimes makes it hard to understand the exact point someone is trying to make. Nevertheless, I find the discussion and particularly the passion surrounding it infectious.