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  1. #31
    Member toddkmiller's Avatar
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    Quote Originally Posted by Youngblood View Post
    Well, it is that time of year again and I thought I would repost my revised spill on vapor barriers.

    Vapor barriers aren't that easy to use if you don't understand what is going on and they aren't that hard to use if you do. Does that make any sense? If it does, you don't need to read any further. If it doesn't, then read on and see if this helps.

    I use plastic or silnylon as a vapor barrier between my hammock and my SnugFit Underquilt. The suspension system on the SnugFit helps keep the vapor barrier against the fabric of the hammock to minimize air gaps that would encourage insensible perspiration to condense and pool. With the vapor barrier held in place against the underside of the hammock fabric, the hammock fabric wicks away any slight buildup of insensible perspiration where it can more easily evaporate and I usually don't even notice it. I pick when I do that and understand how to use it. It is been very effective for me at extending the lower temperature range that I can use my underquilt. I would not use a vapor barrier when I was using the underquilt in warmer conditions because then I would be dealing with sweat and there would be larger amounts of sweat/moisture to deal with as the vapor barrier would cause me to overheat even more and prevent moisture from sweat from passing through the breathable underquilt.

    In general, breathable insulation works best when your insulation is getting too warm for you and less breathable insulation works best when your insulation is not quite warm enough for you. That has everything to do with how, when, and why your body produces sweat (or sensible perspiration) and insensible perspiration.

    Your body produces sweat to help cool off at the outer surface of your skin with evaporative cooling when you overheat. Your body does not produce sweat when you are not overheating... you don't just leak water through your skin all the time. When you are not sweating, your body can produce insensible perspiration to keep your skin from drying out. If your skin is moist enough, or not too dry, your body doesn't produce insensible perspiration because it senses that it doesn't need to.

    It takes energy for your body to produce insensible perspiration. When you are not overheating and your skin is not producing sweat, a vapor barrier will cause your skin to quit producing insensible perspiration after some period of time. Your skin quits producing insensible perspiration because the vapor barrier creates a high humidity environment by trapping the moisture from your previous insensible perspiration. When this happens your body does not use energy to produce that insensible perspiration anymore and can use that energy to help keep you warmer. It a sense, your body becomes a more efficient furnace.

    A vapor barrier is not so good when used at the wrong time or when used incorrectly. When you are overheating and using a vapor barrier, your skin continually produces sweat as a means of cooling off via evaporative cooling. The vapor barrier prevents the evaporative cooling because the sweat is trapped by the vapor barrier. You just keep sweating and moisture can build up. You need to do something to keep from overheating because what your body is doing isn't working because of the vapor barrier. You need to remove the vapor barrier, vent, or remove insulation.

    When you use a vapor barrier with breathable insulation between it and your skin, that breathable insulation is subject to getting moist or even wet from insensible perspiration. The insensible perspiration will initially pass through the breathable insulation and stop when it hits the vapor barrier. This continues until the humidity builds up enough for skin to quit producing insensible perspiration. But until that happens that breathable insulation is going to be getting moist too. What you want is a thin wickable sheet of fabric between you and the vapor barrier such that it can wick any slight moisture buildup away where it can evaporate into the surrounding air. Of course it helps for the surrounding air to be able to absorb that moisture because if it can't, it won't and you will be clammy.

    And of course, if you use breathable insulation between you and a vapor barrier while you are overheating, you will soak that breathable insulation with sweat (sensible perspiration). That is bad and that happens when people don't understand how and when to use a vapor barrier.

    When closed cell foam pads are used with breathable underquilts in hammocks, we get a situation where the overall insulation is greater than the sum of the various components making up the insulation. That is because closed cell foam pads are also vapor barriers. The vapor barrier stops your body from producing insensible perspiration and causes the breathable underquilt to provide more apparent insulation (although it isnít doing anything different) because your body is now operating more efficiently at keeping you warm. If you use a ccf pad that provides 20F worth of insulation with a breathable underquilt that provides 40F worth of insulation by itself, you will end up with more than 20 + 40 = 60F worth of insulation. You might end up with 70F worth of insulation or more.

    You can also wear a vapor barrier to help stay warmer. You can do it selectively for parts of your body or you can do it for your whole body (but donít forget you need to breathe). You can use vapor barrier liners for sleeping bags or plastic bags over your feet, head (as a hat), torso, etc or rain suits. I havenít tried a vapor barrier liner for a sleeping bag but have used a rain suit for a vapor barrier (even breathable ones work) and used plastic bags over feet, head, and torso with success. I always have used thin liner material under them with the understanding they would likely get slightly moist from insensible perspiration.

    Vapor barriers work well for people that know when and how to use them and are often problems or even disasters for people that don't.

    [I am a little conflicted about this particular paragraph. On one hand I feel it is important if this write up is going to be used as somewhat of a reference for vapor barriers. On the other hand I donít want to scare folks about a problem they arenít likely to encounterÖ but here goes.] Understanding vapor barriers, how to use them, when to use them, and when not to use them becomes more important the colder it gets. I donít have experience in extremely cold temperatures but my understanding is that if you use breathable insulation at extremely cold temperatures you risk insensible perspiration condensing inside the insulation as the dew point temperature moves inside the bag itself. Vapor condensing inside the bag creates moisture inside the bag and is just as troubling as sweat or any other moisture getting inside the bag. When this happens the insulation may not dry out at the temperatures you find yourself in and can accumulate over the days you are exposed to extremely cold temperatures. This can be a troubling phenomenon if it occurs as your bag can become increasingly heavier and less efficient. For most of us this isnít an issue as I am referring to extremely cold conditions and we shouldnít be concerned about the dew point moving inside the bag itself at the more moderate cold conditions that most of us camp or backpack in. I only mention it because it should be of interest to the few individuals that are camping or backpacking in extremely cold temperatures.

    Dave Womble
    aka Youngblood AT2000
    designer of the Speer Segmented Pad Extender, SnugFit Underquilt, and
    WinterTarp
    May 13, 2008
    Revised December 1, 2008
    What do you consider 'cold' and 'extremely cold'? To me these are relative terms depending on where you do most of your camping. This would help me get more out of your article.

    BTW, the coldest I have been out hanging is -25C or -13 F. To me that is 'very cold' but not 'extremely cold'.
    Todd K. Miller

  2. #32
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    Quote Originally Posted by toddkmiller View Post
    What do you consider 'cold' and 'extremely cold'? To me these are relative terms depending on where you do most of your camping. This would help me get more out of your article.

    BTW, the coldest I have been out hanging is -25C or -13 F. To me that is 'very cold' but not 'extremely cold'.
    A Canadian asking someone from the deep south what they mean by 'cold' and 'extremely cold'? Good one! Like you say, they are relative terms. While I'm freezing wearing every item of clothing I have, you would probably be standing around in flip flops, t-shirt, shorts, and chewing on ice trying to stay cool. I suspect you would be the better judge at determining when and how to use vapor barriers at 'cold' and 'extremely' cold conditions... whatever they are defined to be. My personal points of reference are probably shifted by 30F from yours.

    What are your thoughts on vapor barriers?
    Last edited by Youngblood; 12-03-2008 at 08:23.
    Youngblood AT2000

  3. #33
    Member toddkmiller's Avatar
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    I have used the HH SS which worked quite well in frigid temperatures. Someone gave me a vapour barrier sleeping bag liner that I may try in the near future. I am a warm sleeper so I think it may be too much. I'm not overly keen on sleeping in my Dri Ducks rain suit either. Your article is very consise and timely since I have to go through this with my scout troop. We recently purchased HH hammocks for the entire troop and are trying to figure out an inexpensive way to make them usable in the winter. Buying 13 HH SS is not in meager budget.

    Any thoughts on the best (and cheapest) material for an under cover? I plan to make some Reflectix pads for each of the hammocks but a non-breathable undercover to slip it into would be a necessity.
    Todd K. Miller

  4. #34
    i don't like the car windshield reflectors if that's what reflectix is, no real insulation, just air bubbles,even with the reflective properties you will likely need more bottom insulation for winter temps, at least that's my experience with the windshield reflector. maybe a good quality ccf like the gossamer gear evazote pad.

  5. #35
    BillyBob58's Avatar
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    I also think your cheapest approach( that would really get the job done) would be CCF pads and a Speer SPE ( or make one). Stack torso segments pretty thick, less so under your legs. Next in expense will be the SS, and then down UQs.

    If y'all can do minus 13*F in a basic SS, I wonder how much CCF you would need? Maybe not all that much.
    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

  6. #36
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    Quote Originally Posted by warbonnetguy View Post
    yb, good thread, now it will be easy for folks to find. question, how many degrees does a vb (non-reflective) add to the low temp of your uq?

    another point, is that i have used a sil shelled synthetic uq several times in several different conditions, and had similar results, maybe even better (no moisture build-up) i think there is a HUGE difference between laying directly on raw ccf and having a vb between the uq and the hammock. it's almost as if it breathes just enough to avoid moisture build-up.

    grizz, here's an idea i've been throwing around for a down uq with a sil shell.

    outer layer shell: sil, inner layer shell:netting or breathable ripstop, second inner layer shell sil sewn only on 3 sides and left open on one end to flip inside-out leaving the breathable shell is exposed for drying. this way, when inside out it has one breathable side, but when right side out, it's sil on both sides. so you have a built in vb, and a sil outer shell for more water resistence.

    i've noticed a difference in full sil uq's and full breathable uq's. if i'm exposed (small tarp) i can feel a gust of cold wind somehow make the uq cold for a second, like it is penetrateing or sucking the heat out. this was not the case when using the sil uq. a good winter tarp probably stops this from happening as well which most will have in cold conditions. i could tell a difference though. it may have been really breathable ripstop i was using, the stuff i have now is parachute 1.1 so it has a very low cfm (air permeability) so i'll have to test it specifically for that and see if it's similar or not, but the sil outer shell would def stop wind well so it might be worth doing, if ysing a winter tarp though, both wind and water resistence may no longer be an issue though.
    I used Frogg Toggs on occasion; usually when sleeping in clouds in the cold, they worked pretty good and I never seemed to suffer any 'excessive' moisture build-up.

    I used the sil shell WBG is talking about and never had any moisture build-up in it the next morning; expected to, but didn't. However, I never really noticed a difference in temps using the shell. The only exception to that would be in high winds under a non-winter tarp when you can actually feel the breeze thru the quilt; the shell almost eliminated that and kept me much warmer than without.

  7. #37
    Hangandy's Avatar
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    Noob Question

    Okay, let me start off by saying I am reluctant in sinking $200 on a UQ yet (especially when I'm not sure what my gear needs really are).

    I purchased a bivy sack online that looks amazing in theory (less than a pound, great strength, strong zippers that open both ends for venting...). Problem is it looks like silnylon and left me drenched inside even with the zipper open a third at the bottom. I'm not sure what use a bivy sack that holds water in would ever be. And then I read this.

    So, If I was to do a rough sewing job and use this silnylon BS ( acronym for bivy sack) as a top shell (wouldn't even cut it up I'd leave both layers in tact) with some insultex or even a medium sleeping bag on the bottom, hook up some shock cord and maybe even a space blanket between the two BS layers, would that work? And then in the summer reverse the thing?

    I've been doing a lot of experimenting and have yet to find anything that works at 0 to -5 Celsius. I even took my old North Face down parka, added loops to it along the zipper line and fashioned a makeshift UQ, and still I'm cold at 6AM.

    In short

    Top layer silnylon (BivySack top)
    Second layer space blanket
    Third layer silnylon (BivySack bottom)
    Fourth layer Insultex
    Fifth layer ripstop nylon (uncoated)

    If anyone likes the idea the junk Bivy Sacks sell all over as "Aqua-Quest" (I wonder if the word Aqua should have given me a hint they might get wet) and you can get them for around $60. They're real use is actually that they truly are waterproof (the company's specialty is actually dry bags). Now before anyone suggests I have a problem using bivy sacks right, I have used the USGI bivy (Goretex) and found it quite good. Only problem is it's a little heavier than I would prefer.

    May just break down and buy a UQ, but I'll probably try to fashion my own first.

    Thanks for the science lessons here everyone!

  8. #38
    New Member AZMike's Avatar
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    Good post. Very informative.

  9. #39
    New Member Yianni's Avatar
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    it is nearly impossible to stop condensation

  10. #40
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    Since it's possible to buy down jackets with DWR outers, and in fact full goretex or eVent down jackets, why not a UQ? Compression for travelling would be an issue, definitely, but I would sacrifice that to be confident that my UQ would be 100% dry. Here in the UK it rains a lot with gusty wind, and unless your tarp is low there is a good chance your UQ is going to get damp/wet. There's also the issue of strap stretching overnight and in heavy rain leading to your UQ brushing the ground depending on how its set up, height from the ground etc.

    A silnylon UQ would not be that easy to manage / manufacture I think, but an eVent one would be much simpler. The problem with a simple DWR would be how to re-proof it unless you just sprayed a fine mist of water on it followed by misting with a graingers DWR product, then straight into the tumble dryer.

    I would certainly be interested in buying an eVent UQ.
    Last edited by NickJ; 03-02-2011 at 05:18.

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