View Full Version : Vapor Barriers VS. "Breathable" Fabrics...
dje97001
02-02-2006, 14:27
Just picked up a book called "the 2oz. Backpacker". Neat little book that contains quite a few suggestions regarding backpacking... The author spends a few pages talking about vapor barriers.
The section suggests that in cold conditions we should consider putting vapor-proof materials in direct connection to the body and put insulating layers outside of that. He states that it will reduce sweating (by keeping the area around the skin near a "naturally" humid state)--unlike putting it over the insulation, which will trap sweat that has been absorbed by the other layers. He claims that you will be warmer too--and won't need such bulky insulation layers.
Further, he writes that putting plastic bags or saran wrap around your feet before your socks AND surgical/plastic gloves underneath your regular gloves or mittens will accomplish the same feat. Warmth without added weight. And slightly damp/humid vs. dripping. Again, he stresses that the vapor barrier heat gain is proportional to the temperature outside (the colder the better).
This sounds fascinating and since his discussion was in-line with that recent Backpacker article on so-called "Breathable" fabrics and their lack of actual usefulness. Ideas? Have any of you used vapor barriers next to the skin (he suggested rain gear, wind shirts or trash bags with holes cut out)?
gargamel
02-02-2006, 15:32
I can imagine this would be working while not beeing active. But what if you start hiking? Wouldn't you instantly get soaking wet under your vapor barrier? I always thought the purpose of wearing wicking layers is to prevent heat loss which is caused when sweat evaporates next to the skin.
That would be true for most fabrics that let air thru. but a vapor barrier such as described above trap the moisture next to skin with no air flow thru, so no heat loss. kinda of lie a dry suit for deep sea diving. pools your fluids around your skin to keep you warm.
fitz
The Will
02-02-2006, 15:43
My only experience with VBLs is in conjunction with a sleeping bag below or at the lower reaches of the bags temperature range. What that author says is counter intuitive to me and I usually try to do much the opposite. When using a VBL I wear long underwear and even gloves to prevent any skin from touching the VBL. Simply using the VBL is going to increase the humidty of the skin. The long underwear spreads the moisture and prevents your skin from coming in direct contact with the plastic-like, humid VBL.
As far as creating an additonal heat factor, it is true and effective. VBLs drastically reduce the amount evaporative heat loss.
sparky2000
02-02-2006, 15:47
This is more confusing then useful. Wet feet are wet, therefore, the plastic will keep them from wicking and the feet will continually be wet and wetter.......I can't emagine this thought
Just Jeff
02-02-2006, 16:08
Well, they don't really get wetter and wetter because they stop sweating at a certain humidity level (at least when you're stationary...which is when most people use vapor barriers). I've only used the socks and they made a big difference...but I wouldn't put them right next to my skin. I used a thin liner sock, the VB, then a heavy hiking sock to provide loft.
Obviously, as your body heat increases you'll need the protection of the VB less...like when you're active, for example. Vapor barriers are only one component of a moisture management strategy that must be adaptable for various environmental conditions, body factors and activity levels. Like the book said - it's effective in cold, dry conditions.
Breathable fabrics serve a completely different purpose, IMO. They give weather protection OVER lofting layers to protect the insulation, while still allowing perspiration to evaporate from the system. In some conditions (like when you're active or if it's too warm for a VB), that's more important than stopping evaporating cooling.
dje97001
02-02-2006, 16:15
Yes, but the socks will be bone-dry (perhaps this would be like having liner socks?).
I don't claim to understand it either--and I'm not blindly believing it because it does sound counter-intuitive. I can make guesses/statements on both sides that *seem* intuitive, but I am curious as to whether anyone has had actual experience with this--vapor barriers as a base-layer. :confused:
Just Jeff
02-02-2006, 16:28
No, the liner socks get moist (but not wet). The outer socks could be wet or dry depending on what you're doing.
VBs for sleeping bags are very effective in cold weather. If you sweat at night (or just give off insensible perspiration), it'll evaporate into your bag, then freeze before it leaves your bag. After several days, your bag will get pretty heavy and you'll lose loft. Lost loft = cold nights, so the VB protects your loft. There are stories of Iditarod racers bringing back 60 lbs sleeping bags because they didn't have a vapor barrier.
Oh - I just re-read your last statement...you're asking specifically about putting the VB against the skin w/o any kind of wicking layer next to the skin. Sorry for not seeing that in your first post!
I've never seen recommendations to put it right next to the skin as a base layer - so that's kind of confusing. HOWEVER, all VB technology says to put it underneath the insulating layers. Otherwise, the VB will cause your sweat to saturate the insulation. Most say use a light base layer to make it more comfortable, then put insulation, then some kind of environmental protection for the insulation. For example, Stephensen's VB gear is coated with "fuzzy stuff" to act as a wicking layer against the skin.
dje97001
02-02-2006, 16:35
JustJeff-- yeah I just stumbled on http://www.warmlite.com/vb.htm. It sounds to me like the wicking vs. vapor barrier debate has probably already gone through several iterations... phases, perhaps they are each fads with their own disadvantages and advantages. I am curious as to why most sleeping bag manufacturers wouldn't incorporate vbl. In that particular application it does sound like "common sense" whereas in the rest of them it sounds hard to believe. Very odd...
dje97001
02-02-2006, 16:47
it looks like someone at Field-and-Stream thinks vapor barriers are pretty useful... but primarily in below-zero temperatures...
http://www.fieldandstream.com/fieldstream/outdoorskills/article/0,13199,396707,00.html
gargamel
02-02-2006, 17:02
it looks like someone at Field-and-Stream thinks vapor barriers are pretty useful... but primarily in below-zero temperatures...
http://www.fieldandstream.com/fieldstream/outdoorskills/article/0,13199,396707,00.html
Sounds very reasonable. Having the choice between cold & dry and warm & wet I would choose the latter. The most interesting thing in this article is the fact, that our body produces perspiration in cold and dry weather to maintain surface humidity (probably to protect the skin from drying out).
Thank's for digging this up.
Using VBLs when hiking requires the user to judiciously modify insulation to never overheat, otherwise you would be uncomfortably wet inside. I've only known a few people to use vapor barrier shirts. I do use plastic bags on my feet, over the liner sock and below the insulating sock, when xc skiing below about 10F because my feet will have trouble staying warm otherwise. It's not so much that it makes your feet warmer immediately, but it keeps the outer sock dry so your feet will not chill during the late-day downhill run. In a sleeping bag, as someone already said, the advantage is really on multi-day trips to avoid moisture accumulation in the bag.
icemanat95
02-03-2006, 11:23
Maintaining surface humidity is only one part of the prupose of sweat. The other side is to get rid of excess body heat.
The problem with the VBL against the skin theory is that when activity levels bring body temp up, the VBL inhibits the body's normal means of regulating that heat. Getting rid of the VBL layer requires you to strip down completely, which then puts you in peril from exposure to the extreme cold. Your alternative is to remove an insulating layer to shed heat, but the moisture against your skin conducts heat rather nicely now that the cold can get to the VBL more readily. So really your best method, when using vbl underwear, is to regulate your body heat by regulating your level of exertion.
I'm not universally trashing VBLs, they have their uses. I have a sleeping bag vbl for winter use and vbl liners for my mountaineering boots (I wear them over lightweight liners and under my insulating socks. But I cannot imagine the conditions that would have to exist to induce me to wear vbl underwear. The clamminess would be unbearable.
gargamel
02-03-2006, 13:53
Maintaining surface humidity is only one part of the prupose of sweat. The other side is to get rid of excess body heat.
But this was the really interesting part, at least for me. Almost everybody knows that sweating generates a heat loss through evaporation. This concept is easy to understand. But that you also can get wet in cold and dry conditions, even if you don't generate excess body heat, was pretty new for me.
I absolutely agree on the clamminess part. But I'm sure there are a few who would put up with this for the benefit of saving a couple of ounces. It's only a matter of time if we see the first multiple trash bag wearing ultralighter. This would cast an entirely new light on the term "Hiker-Trash" :D
This is a question that I had since coming back from my first winter hike 3 or 4 weeks ago. I had 0’ down bag inside of “breathable” bivy. I woke to a mess of condensation inside of my bivi and someone suggested a vapor barrier. So is it anything more than a glad bag?
Just Jeff
02-03-2006, 15:41
Was there a space between your bag and bivy?
Here's what happens with a normal bag:
- Your perspiration evaporates from your body and into your bag
- If the temperature is warm enough, it then evaporates out of the bag
- If the temp is too cold, it can condense inside the bag or on the outer surface of the bag
Now introduce a bivy:
- The temp of the bivy's fabric is likely lower than the temp of the bag. This often happens in bivies that have a space between the bivy and bag
- Your perspiration evaporates out of your bag, and condenses on the bivy fabric b/c it's colder than the bag's fabric
Making sure the bivy is directly in contact with the bag can help. But as has been mentioned, the difference in temp and humidity between inside your bivy and the environment is the key.
So given that, if you want to keep all of your body's moisture out of your bag, a VB liner inside the bag (or clothes to accomplish the same objective) is the only way I know of. At least with clothing VBLs you can add worn insulation (outside the VBL) to increase the loft you sleep in.
gargamel
02-03-2006, 15:49
Making sure the bivy is directly in contact with the bag can help. But as has been mentioned, the difference in temp and humidity between inside your bivy and the environment is the key.
So given that, if you want to keep all of your body's moisture out of your bag, a VB liner inside the bag (or clothes to accomplish the same objective) is the only way I know of. At least with clothing VBLs you can add worn insulation (outside the VBL) to increase the loft you sleep in.
Shouldn't a Gore-Tex bivy be breathable enough to let the moisture through? And if not would it then be better to put the bivy inside the sleeping bag (moisture goes through bivy into the bag and evaporates slowly) ?
Just Jeff
02-03-2006, 16:12
Well, yes and no. Under the right conditions it'll work great (though some materials are more breathable than gore-tex). But no gear will work in all conditions. If the humidity outside the bivy equals the humidity inside the bivy, NO wp/b fabric will pass the vapor.
Also, if the temp of the bivy's fabric is low enough to allow condensation before the vapor passes through, the material won't matter. This is why the space between the bag and bivy makes a difference - it allows the vapor to cool, and allows the bivy's fabric temp to decrease.
Putting a wp/b bivy inside the bag might add some heat and restrict the amount of vapor moving from your body into your bag a bit, but then you lose the protection from the outer elements (like rain, dew, etc).
Like every other piece of gear, bivies are a trade-off. Ventilation is probably the best answer to reducing condensation, and bivies aren't very good at that. However, they're very quick and easy to use and suit certain conditions very well...they can literally be a lifesaver in some situations. It seems that most hikers who use bivies have highly breathable, water resistant materials to protect bags under a tarp from spray and dew, rather than truly waterproof bivies that can act as a stand-alone shelter.
FWIW, I'm tinkering with a wp/b hammock bivy design...if I ever get around to making it I'll post my findings back here.
I don't claim to be an expert on bivies, though - I've only used two types (a wp/b ID Salathe and a non-breathable Wiggys). And a military poncho and the JRB Weather Shield, if you can count those.
gargamel
02-03-2006, 17:08
Sounds fairly plausible. I normally use my bivy as an emergency shelter for day hiking in alpine conditions. It's a relatively lightweight alternative for carrying a tent (way to heavy) or a tarp (useless above tree line). For my thruhike this year I intended to carry it not as weather protection (I'll go with a tent), but only as an additional layer, as my sleeping bag is only rated down to 20 degree. By putting it in my bivy I had hoped to gain some additional cold protection. Seems I would be better of if I would exchange it with some other type of liner or something else in the same weight range (14 oz).
Thank's for your input :)
i'm going slightly sideways on this, as it only concerns boots and feet, which are my only experience with vapor barriers.
when i was in in the army, stationed at fort drum, ny (winter lows in the minus 40s at least some of the winter), we would occassionally use what are known as mickey mouse boots... they are these huge black or white rubber boots that made the wearers look like the cartoon character... i'm sure you all know what i'm talking about. those boots were officially known as "VB Boots". they were entirely rubber, and designed with a large airfilled sole, for insulation. mostly, they were designed to be used on guard duty, or other stationary jobs. but our ski and snowshoe bindings were all made to fit over them. they are the ONLY things that would keep your feet warm in those conditions. i grew up just south of Ft Drum, in syracuse. winter lows there were usually a little warmer, maybe in the minus 30s at times... sorel-type boots, with the felt inner liner, were ok, but not all that warm for extended outside use.
the VB Boots were frequently blamed by cold-ignorant officers (ie, folks who grew up in the south, and who had NO cold weather experience) for causing cases of frostbite among equally cold-ignorant (again, southern) troops. this was because your feet would sweat, get wet, and freeze when you stopped moving or took the boots off. the key was to carry a towel. you had to dry your feet off frequently, change socks about once every couple hours (hanging them inside your jacket, where they could dry out), and understand that getting the feet wet was just part of the system... you couldn't do one (wear the boot) and not the other (dry off your feet and change socks). as long as you changed socks and dried off your feet (oh, and dried out the boot with the towel), you would be fine.
however, our Virginia-bred commanding general, unable to understand that people sweat at different rates, outlawed their use and we were relegated to wearing matterhorns. they're a leather (read 'wet') thinsulate (read 'cold') lined boot that didn't work too well under 40*... i never got frostbite, but did come very close on several occassions. those were some of the coldest winters i ever spent doing military training.
all that said, i think the principle would apply to sleeping bags as well... eventually, you would stop sweating, and the VB would prevent your insulation from getting wet. but you'd have to towel off in the morning.
RedneckRye
02-03-2006, 18:38
Western Mountaineering makes a VBL bag liner, I think it is called the Hot Sack. Has anyone one out there used one?
This question is kind of along the line of the topic.
I notice that I get cold at night at home when I go to bed with wet hair.
My thinking was that I could take a thin plastic shower cap to put on over wet hair at night when I sleep. This would act as a vapor barrier and keep my head warmer and therefore my whole body would feel warmer.
Is this a crazy idea? Does anyone think it will work or have any alternate ideas. I sleep cold and am very concerned about hypothermia on my upcoming thru hike.
gargamel
02-03-2006, 19:29
This question is kind of along the line of the topic.
I notice that I get cold at night at home when I go to bed with wet hair.
My thinking was that I could take a thin plastic shower cap to put on over wet hair at night when I sleep. This would act as a vapor barrier and keep my head warmer and therefore my whole body would feel warmer.
Is this a crazy idea? Does anyone think it will work or have any alternate ideas. I sleep cold and am very concerned about hypothermia on my upcoming thru hike.
The question is why you would go to bed with wet hair?
In general to put on some sort of headdress is not a bad idea as 70% of heat loss takes places on your head. But I think a fleece hat would be more pleasant to wear than a shower cap (although the latter may look much cooler :D )
If it rains heavily and I am hiking, pretty much everything gets wet just from sweat. I have semi long hair and it may be hard to have it air dry before bed. If it's cold out I'm concerned about getting cold. Maybe a fleece hat would work but wouldn't it get all wet and then I will get cold?
How do you veterans deal with this or is it never an issue?
I know I sound totally naive here but I am a weekend backpacker that's headed out on a long distance hike and I want to be prepared.
And yes, a shower cap would look crazy. I would certainly earn a crazy trail name if anyone saw it.
gargamel
02-03-2006, 19:59
Although no "veteran" I would try to dry my hair with a towel as much as possible and then put on a fleece hat.
Thanks for the advice! I'll leave the shower cap at home. LOL
Just Jeff
02-03-2006, 20:16
For my thruhike this year I intended to carry it not as weather protection (I'll go with a tent), but only as an additional layer, as my sleeping bag is only rated down to 20 degree. By putting it in my bivy I had hoped to gain some additional cold protection.
At 20 F, it should be pretty dry outside your bivy since the moisture will freeze and fall to the ground. A bivy might work well in that situation.
I haven't thru-hiked yet, but it seems that not many carry a wp/b bivy on a thru. Maybe they find it's not worth the weight? Or maybe using a 10 oz DWR bivy or a bag liner is enough for them. Dunno...any thru's have an opinion on this?
The Will
02-04-2006, 21:57
For my thruhike this year I intended to carry it not as weather protection (I'll go with a tent), but only as an additional layer, as my sleeping bag is only rated down to 20 degree. By putting it in my bivy I had hoped to gain some additional cold protection. Seems I would be better of if I would exchange it with some other type of liner or something else in the same weight range (14 oz).
Thank's for your input :)
I carried a bivy on my thru. It was, aside from lean-tos, my primary shelter. You can expect it to increase your warmth, largely because it is keeping the air around your sleeping bag still and thus minimizing heat loss through convection. If you are in the enclosed environs of a tent, I'm not sure the benefit would be as measurable and maybe for the same weight, a fleece bag liner may be for effective.
That would be true for most fabrics that let air thru. but a vapor barrier such as described above trap the moisture next to skin with no air flow thru, so no heat loss. kinda of lie a dry suit for deep sea diving. pools your fluids around your skin to keep you warm.
fitz
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"deep sea" diving? he he, ah no. - That's not how a drysuit works. As I wear a drysuit often daily, I know. The outer shell of the drysuit does only two things, protects itself from leaking and keeps the water OUT. Good drysuits (unlike wet suits) have little thermal insulation capabilites. Why? Because in the "deep sea," (he he) pressure CRUSHES the suit (and the diver).
That's why all dry suits have an inflation system to inject air into the suit so as to create an insulating AIR layer. Inside the suit, you wear some moisture wicking garmet that actually traps your body heat - exactly the opposite of what this article espouses. Since the outer drysuit layer is impermiable, sweat will collect in the suit. Most pros lean to wear sweat bands around their ankles to catch the sweat when it comes out of the foot pouches.
As for wearing vapor barriers next to skin, you will be one miserable camper - especially while moving with a pac, particularily if you have - like most men - body hair. Put bags on your feet and you won't be walking long. I know from experience as I have twice been deployed above the artic circle. (and the platic bag on your feet is a fast way to lose your feet in sub freezing weather.) :cool:
Instead, we used womens knee high stockings (some even used panty hose), then the normal artic issued wool socks (There is no Army Issue capalene). The stockings with rigid foot care actually work quite well. (hey, if it works and I don't have to have toes amputated, who cares?)
A lot of this sounds like the theoretical musings of an arm-chair hiker. IMO, and it's just my opinion. I do not see "ultra-lite" as a form of self flagulation/punishment.
There is a thing as being too "ultra lite." For me, I do not see the need to make myself miserable or risk life and limb because some crackpot - who probably doesn't even hike - is caught up is some hyped fad.
For the record, "Vapor" barriers remove some vapor but little if any sweat. So some sweat will escape to the wicking layer (where body heat converts it to vapor in theory so it can escape the "Vapor" barrier). Without the wicking layer, the inside of the "Vapor" barrier will be drenched in sweat which for most folks is not a good thing - in low temps, it can be fatal.