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  1. #41
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    So...newb question on the subject.

    From a clothing perspective, you wear different layers to accomplish different things to keep yourself warm in a cold environment.

    Closest to your skin is a wicking layer, like UnderArmour. The intent is to pull the moisture away from your skin, preventing cooling and/or overheating.

    Next are insulation layers...often wool that has good insulative properties even if wet.

    Then the outside layer is the vapor/wind breaking barrier. It prevents moisture from reaching the insulative layers, and prevents the wind from pulling warm air from them as well.

    Why wouldn't you layer in the same fashion in a hammock?

    Seems to me that you'd want to have some kind of wicking agent if possible closest to your body...then your insulation layer(s), and on the farthest outside your vapor barrier. So I'd assume that your vapor barrier/windbreak would be OUTSIDE of your UQ, not between the UQ and hammock.

    This is assuming that the vapor you're trying to avoid is coming from outside moisture, not sweat. Sweating would be avoided by temperature regulation inside the hammock/sleeping bag/TQ and clothing, I'd think.

    Again...I'm a newb...asking a newb question.

    Where am I wrong, and why? Thanks!

  2. #42
    Senior Member ChrisH's Avatar
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    Have you seen DeJoha's vapor barrier illustration? If not, here is the link...
    http://www.hammockforums.net/forum/s...ad.php?t=26191

    Hope that helps

  3. #43
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    I'm not convinced by this (or possibly just not getting it). If you are sweating then your body is too hot, yes? in that situation the vapour needs to go somewhere. If it doesnt, it either condenses somewhere and causes a problem, or you just get hotter. Surely it has to be a very fine line where a VB would actually work, or rather a very narrow band of temperature/microclimate. Would it not be better to ensure that you're not sweating in the first place and so prevent the problem?

    At the weekend I noticed that the inside of my tarp was very moist. It was a good away away from the hammock, and the hammock has a breathable top shield. The wind had been strong in the night, though the tarp (WB superfly) had both doors closed and about 8 inches of space to the floor. It had rained very hard during the night, and I figured that the condensation on the tarp was simply the result of the temperture difference between the inside and the outside of the tarp, and the fact that the air was very moist. The ambient was around 4 degrees C at a guess. I was warm and not sweating with the combination of north face blue kazoo bag (used as a TQ) and an HG winter burrow UQ. I was wearing Woolpower thermal top and longjohns.

    I've read the text and looked at the diagram, and it's not making sense to me (yet). I can't understand why this is neccessary when if you're sweating too much you need to either vent something or wear less clothes, not use a VB, a VB is going to make you sweat more UNLESS you are cold to begin with and as you warm up the VB helps that process, but ultimately you're going to overheat / create a pile of condensation on the VB unless you vent.

    You want vapour to be dispersed yet the air between you and your insulation to be warm, you dont want any risk of moisture creation inside the hammock, and the best way to avoid that is to have windproof/breathable material. Isn't it?

  4. #44
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    Quote Originally Posted by Owl View Post
    So...newb question on the subject......................

    Seems to me that you'd want to have some kind of wicking agent if possible closest to your body...then your insulation layer(s), and on the farthest outside your vapor barrier. So I'd assume that your vapor barrier/windbreak would be OUTSIDE of your UQ, not between the UQ and hammock.
    Newbie questions welcome! And certainly things concerning vapor barriers are high on the list when it comes to confusion. And using vapor barriers while not understanding them will probably leave you wet and cold. It seems to me the system you are describing (A true VB over (outside) all of the insulation but NO skin level VB) would end with a cold and wet person. I'm fairly sure the system you are describing – probably one you have been using – does not have a "vapor barrier" for the outer layer. (Correct me if I'm wrong) it probably has what is known as a waterproof breathable (WPB) outer layer like some form of Gore-Tex. Now people argue about how breathable these WPB's really are, but I can guarantee you that they are no match for something like Sil-Nylon when it comes to blocking vapor. These WPB's are meant (designed) to hopefully block liquid water from the outside (not necessarily outside vapor) and to allow water in vapor form on the warm inside to pass through. A true vapor barrier is both waterproof (blocking the passage of sweat or rain) as well as blocking water in vapor form. If your body's vapor (insensible perspiration) cannot get past the vapor barrier, then it cannot reach the outer layers of cold insulation and condense in them.

    Want to know for sure if you have an actual vapor barrier for your outer layers? Take your jacket (again probably a WPB) and put it on next to your skin or over a T-shirt and sit down in your easy chair. Or maybe walk around at a mild level of exertion on a cool day. Most likely, you're pretty comfortable as well as dry. Now take that jacket off and put on a large garbage bag to which you had added holes for your head and arms. Feel the difference? Even just sitting still in your easy chair, it probably won't take but a few minutes until you feel that dampness. Sit outside on a cool day, when it's very unlikely that you will sweat, and you will still feel the dampness with that garbage bag. That is a vapor barrier. If you put such a thing only on the outside of your insulation, it won't be long before that insulation is wet even if you are sitting perfectly still and feeling on the cool side. No sweat is necessary for this wet insulation, only enough time.



    This is assuming that the vapor you're trying to avoid is coming from outside moisture, not sweat. Sweating would be avoided by temperature regulation inside the hammock/sleeping bag/TQ and clothing, I'd think.

    Again...I'm a newb...asking a newb question.

    Where am I wrong, and why? Thanks!
    The moisture we are trying to avoid is not coming from the outside, and it is probably not even from sweat. It is your body's insensible perspiration. A very thin layer of extremely high humidity that your body produces to help keep your skin from drying out for one thing. This layer of high humidity is pretty much always present whether or not you are approaching overheating and sweating. It's like the vapor that comes out of your mouth every time you exhale. Even if you on the verge of hypothermia, if you breathe on a very cold surface that is very close to your mouth, your breath (vapor) is going to condense into liquid when it hits a cold enough surface. And that cold surface can be the outer layers of your insulation or rain garment. Sweat is an entirely different matter. Sweat is not necessary for you to get condensation in your sleep system, just like you can get condensation on the inside of your tarp even if you are nowhere near overheating.

    However, if you do manage to sweat a bit inside your vapor barrier, that moisture should also be prevented from reaching your insulation layers. But it will obviously be better and more comfortable to learn to recognize the "overheat" situation and vent as needed.





    Quote Originally Posted by NickJ View Post
    I'm not convinced by this (or possibly just not getting it). If you are sweating then your body is too hot, yes?
    Yes!

    in that situation the vapour needs to go somewhere.
    Sweat is not vapor, it is liquid. Your body produces this liquid which then is supposed to evaporate ( go from liquid to vapor ) and cool you down by the process of evaporative cooling. But even if you do sweat, then it does need to go somewhere, but hopefully not into your insulation. Hopefully it will be contained inside the vapor barrier.

    If it doesnt, it either condenses somewhere and causes a problem, or you just get hotter. Surely it has to be a very fine line where a VB would actually work, or rather a very narrow band of temperature/microclimate. Would it not be better to ensure that you're not sweating in the first place and so prevent the problem?
    It's certainly better to ensure that you're not sweating, but that might be easier said than done when you're asleep. However, you don't have to sweat for your body's insensible perspiration (vapor) to cause mischief in your sleep system or other insulation items.

    At the weekend I noticed that the inside of my tarp was very moist. It was a good away away from the hammock, and the hammock has a breathable top shield.
    Exactly. And there was no sweating required from you in order for that tarp to get wet, right? All that was needed from you (or from some other source) was some vapor floating through the air which could then condense on the cold tarp surface (vapor barrier).

    The wind had been strong in the night, though the tarp (WB superfly) had both doors closed and about 8 inches of space to the floor. It had rained very hard during the night, and I figured that the condensation on the tarp was simply the result of the temperture difference between the inside and the outside of the tarp, and the fact that the air was very moist. The ambient was around 4 degrees C at a guess. I was warm and not sweating with the combination of north face blue kazoo bag (used as a TQ) and an HG winter burrow UQ. I was wearing Woolpower thermal top and longjohns.
    Plus, especially with those doors closed, any warm vapor that you were contributing from your body and (mostly) your breath could not rapidly escape from inside the tarp, and naturally condensed when it hit the cold tarp surface – a vapor barrier. No doubt there was plenty of humidity adding to the problem, but the vapor that you were producing inside the tarp was probably also a factor.

    I've read the text and looked at the diagram, and it's not making sense to me (yet). I can't understand why this is neccessary when if you're sweating too much you need to either vent something or wear less clothes, not use a VB, a VB is going to make you sweat more UNLESS you are cold to begin with and as you warm up the VB helps that process, but ultimately you're going to overheat / create a pile of condensation on the VB unless you vent.
    Sweat is not the issue, insensible perspiration and vapor is. Although, if you sweat without a vapor barrier, then sweat is also part of the problem. Even the effect of sweat on your insulation will be greatly reduced by a vapor barrier. You are right, you want to avoid sweat with or without a vapor barrier being close to your skin. You will not sweat inside a VB unless you over heat, but you will feel damp. Once you reach 100% humidity at skin level, your body stops producing more vapor. But it feels like sweat, but in my experience it only goes so far and then gets no damper. But if you over heat- with or without a VB- you can keep right on producing sweat as your body tries to cool itself.

    You want vapour to be dispersed yet the air between you and your insulation to be warm, you dont want any risk of moisture creation inside the hammock, and the best way to avoid that is to have windproof/breathable material. Isn't it?
    Condensation can occur even with breathable materials. Over the years many a person has reported how their breathable insulation often gets heavier and heavier on multi-day trips in very cold weather. I have a friend who has reported problems with that even with temps only in the 30s at the coldest and on other trips with lows no more than the higher 40s. This was all with breathable gear. However, condensation is virtually guaranteed with a true vapor barrier. So you must make sure that if you have a true vapor barrier (a waterproof shell) outside of your insulation layers, that there is another vapor barrier between you and your insulation. What ever insulation is between you and any vapor barrier is most likely going to get wet. The only exception I know of to this is when I use a space blanket directly under my hammock but on top of my HHSS insulation, or under my hammock inside of a Peapod. ( though there is not much insulation between me and that VB, only what I am wearing) There is still possible condensation under these circumstances, and I have from time to time seen a couple of drops on top of the space blanket, but not much. Supposedly that is because being that close to my skin( though not tight against it), and surrounded by the outer insulation, the space blanket (VB) is kept close to body temperature. So condensation against a cold surface should be minimal, and apparently it is. And apparently since it is only under my back and not surrounding my body, most of my insensible perspiration manages to remain vapor, and work its way out of the breathable topside. That's how it is work for me, anyway, both warmer AND dry.

    I would say that VB theory is pretty solid and practical in the real world. Though it will make matters worse if used incorrectly. So anybody using it should make sure they understand the theory, and hopefully do some experimentation under very safe circumstances. Do a search here for Wisenber's fairly recent posts on VB use. Quite impressive indeed! It seems he added at least 20*F to his insulation's abilities, plus kept it dry. (Maybe some of his posts are in this thread?) Because a VB does not just keep your insulation dry, it halts a major form of heat loss: evaporative cooling.
    Last edited by BillyBob58; 03-02-2011 at 10:21.
    For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.
    Romans 8:18,21-22

  5. #45
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    Thanks Billy. The science makes sense, but the practicality doesn't. In your final paragraph re getting another 20f, why not just wear slightly thicker thermals? (for example) Rather than run the risk of high moisture inside the hammock?

  6. #46
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    Quote Originally Posted by BillyBob58 View Post
    ...it halts a major form of heat loss...
    An adiabatic system would be appropriate for cold blooded animals, but not for us. We cannot survive if we accumulate heat.

    Just sayin'...
    Last edited by MacEntyre; 03-03-2011 at 05:47.
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  7. #47
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    Quote Originally Posted by NickJ View Post
    Thanks Billy. The science makes sense, but the practicality doesn't. In your final paragraph re getting another 20f, why not just wear slightly thicker thermals? (for example) Rather than run the risk of high moisture inside the hammock?
    You are welcome Nick! And yes, another way to increase the warmth is to wear thicker LJs or just spend more money, weight and bulk on thicker insulation. Though frankly, I doubt that just having slightly thicker thermals would get me another 20*F, though who knows maybe for some. Also, when I use VBs, I end up with less moisture in both my hammock and my insulation, but it's true YMMV.
    Note post 26 and 32 in this thread for example: http://www.hammockforums.net/forum/s...zzy#post387077

    Also note the posts here- even on a short trip- comparing much less water weight even though the VB protected MW4 was NOT dried in the Sun for 4 hours:
    http://www.hammockforums.net/forum/s...t=Fuzzy&page=3

    Also, post #6 in this thread is interesting:
    http://www.hammockforums.net/forum/s...light=Warmlite

    So, I could skip the $3, ~ 2 oz space blanket in my HHSS ( which I think gets me at least 15F, maybe more) and just use a second HH pad. Instead I would then have ~ 8 oz added and 30 plus $ and way more bulk.

    But, that still would do nothing for the condensation issues. Most of us do great most of the time with our breathable systems. We get away with it just fine. But there are still folks who on week long cold trips report loss of loft in their down gear- and/or loss of warmth in synthetic gear- due to condensation inside their breathable insulation. I have heard about it many times over the years, and I have seen it happen with a friend of mine's PeaPod on 2 different week long trips. Though it didn't happen with my PeaPod, protected with a VB. Apparently 100% loft after one very wet week with no sunshine. It has worked well for me and others.

    But don't get me wrong, I'm not trying to talk any one into VBs. Matters not to me. HYOH and all like that! And except for a space blanket (VB) under me in an HHSS or sometimes in my PeaPod, I mostly use breathable systems any way. But questions were asked, and it seemed there was some confusion on what a VB was meant to do, so I tried to explain to best of my limited ability. I hope it was of some help.

    Although, I have never forgotten my 1st VB observation, over 20 years ago. I had a friend whose feet were freezing. One pair of wool socks, then another, still freezing. I loaned him my Patagonia VB socks which I had never even used. He put them on with one layer of wool socks over them. It didn't take very long until he told me " Oh Yeah, my feet are toasty!". Lesson learned.

    Edit: Oh, and I forgot: If you choose to use a truly water and wind proof outer layer, like a 2Q sil-nylon UQ protector or the HHSS Undercover, you had better use an inside VB right under or pretty close to your hammock or you are going to have some serious condensation issues.



    Quote Originally Posted by MacEntyre View Post

    Originally Posted by BillyBob58
    ...it halts a major form of heat loss...
    An adiabatic system would be appropriate for cold blooded animals, but not for us. We cannot survive if we keep accumulate heat.

    Just sayin'...
    Mac, I might be missing your point. Can you elaborate? Are you saying it might not be good to block evaporative cooling during a cold nights sleep, that it might be a problem? Or something else?
    Thanks,
    Bill
    Last edited by BillyBob58; 03-02-2011 at 22:18.
    For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.
    Romans 8:18,21-22

  8. #48
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    Quote Originally Posted by BillyBob58 View Post
    Mac, I might be missing your point. Can you elaborate?
    Just sayin' that we need to control heat loss, not eliminate it. It's a balance determined by this equation:

    Input - Output + Generation = Accumulation

    We seek to control the Input, Output and Generation of heat so that our Accumulation is zero. That way, we remain warm and do not heat up.

    Input is external warmth brought in, such as a fire.
    Output is heat loss, controlled by insulation.
    Generation of heat is from metabolism, primarily controlled by activity, secondarily by eating.

    We could eliminate Output from the equation by assuming adiabatic conditions, or perfect insulation that stops all heat loss. Then it would read:

    Input + Generation = Accumulation

    Let's say that we have no Input from external heat sources, so that term is zero. Then, whatever heat we generate, we accumulate. We cannot lower our metabolism to generate zero heat, or we will be DRT. So, if we constantly generate heat, our temperature will always increase.

    Therefore, we cannot utilize an adiabatic insulation system that completely eliminates heat loss. Unless our insulation is inadequate, we must lose heat.

    - MacEntyre
    Last edited by MacEntyre; 03-03-2011 at 06:43.
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  9. #49
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    I think Mac was making a joke that went over peoples heads when you made the comment it halts a major form of heat loss. As Mac points out, we have to lose some heat to survive... so the joke is to be careful and not get your insulation system so efficient that you die from over-heating from your own body heat.

    But back to the very good vapor barrier discussion. There are times when vapor barriers are a problem, times when they are great, and there are times when they are kinda, sorta, okay. I tried to touch on some of that in the first post on this thread and it might help some of you with the questions to read it again. Sometimes you need to read something, think about it, maybe try some things and get a little experience with it, and then go back and read it again and see if you have a better appreciation/understanding.

    In moderate conditions that allow it, breathable insulation that doesn't absorb moisture is hard to beat because it offers comfort over a wide range of temperatures. It does this because it handles overheating and sweat issues so well. But with everything we have available, there are tradeoffs. That very breathable insulation that is so comfortable, like a fleece jacket, can't handle wind. And that's the story of insulation... there is not one scheme that is best for all the conditions you will likely encounter while being outdoors.

    Just to handle rain as a long distance backpacker, you need to be flexible. Sometimes you might just get wet as your body temperature is balanced out by the cooling rain. Other times you might want to use an umbrella to stay dry and not overheat. Then other times you may need just a rain jacket with a hood. Then if is windy/cool enough you may want those rain pants on and those water proof gloves. You need to use the right thing at the right time or it will absolutely sux out there and you might swear at that sauna suit you bought thinking it was rain gear, for example.
    Youngblood AT2000

  10. #50
    MacEntyre's Avatar
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    Yeah, sorry... joke was a bit dry, and ivory tower like... but based on sound principles.

    Warm, breathable, windproof, waterproof, lightweight, inexpensive... we can have some, but not all.
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
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