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My Thoughts on Vapor Barriers... again

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  • Dave Womble
    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
    Message 1 of 5 , May 13, 2008
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      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 I will see if I can make it make sense for you.

      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

      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 you 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

      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.

      Dave Womble
      aka Youngblood AT2000
      designer of the Speer Segmented Pad Extender, SnugFit Underquilt, and
    • Cara Lin Bridgman
      I think another consideration for vapor barriers is ambient humidity. It s not just your own body producing sweat that makes them work. They also rely on the
      Message 2 of 5 , May 13, 2008
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        I think another consideration for vapor barriers is ambient humidity.
        It's not just your own body producing sweat that makes them work. They
        also rely on the material wicking away moisture--or being dry at the

        With a vapor barrier, if you start out too wet, you won't
        dry--especially when it's extremely humid.

        So, I'm not convinced vapor barriers work under rolling fogs, typhoons,
        and other extremely humid conditions--all are damp, cold, and
        hypothermia inducing.

        The Appalachian Mountains have often been called a Temperate Rain
        Forest. In Taiwan at the elevations where I hike (2000-3000 m), the
        mountains are Temperate Rain Forest, too. Because the ambient humidity
        is so high, Taiwan's hikers tend to carry down bags rated for much
        colder temperatures than expected. This is because the humidity
        permeates everything and affects loft. Under these conditions, damp
        clothes, if slept in, usually do not dry. So, I make sure I pack
        sleeping clothes (including socks) in the same bag as my sleeping bag
        and I change into these clothes right before bedtime.

      • Blake Robert
        I invited people on this list to go---here is how it went. An irony about my ascender as hammock end clamps---we just had one of our two gear swaps at Four
        Message 3 of 5 , May 13, 2008
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          I invited people on this list to go---here is how it

          An irony about my ascender as hammock end clamps---we
          just had one of our two gear swaps at Four Seasons
          Outfitters---I went on the hike instead---but, one of
          our members sold her 1990's Jumar ascenders for $10.

          I wish I had asked what she would be asking!

          1.) Les has had some changes in his plans for the end
          of the week. He can no longer go in to the camspite at
          Dave Joy Point Thursday---not until late Friday. While
          this would enable me to camp out Friday night and save
          the best campsite for you folks---I do not feel that
          Les should have to go in Friday afternoon/night and
          come back again in the morning---so, I suggest we just
          assemble at 8 a.m. Saturday morning-load up and go
          out. No flagging. Les could be the only one driving

          I have not heard from Les that the current snow fall
          will affect our plans. If there is any concern about
          the road conditions-we could reverse the Dave Joy
          Point and Pumphouse Wash schedules.

          More later?????????

          2.) I picked Katarina up at her dormitory on the NAU
          campus and drove down to the Wet Beaver trailhead.
          Here, we were soon joined by Mary/Sedona Meg and
          started in. The recent rainfall had allowed ocotillo
          to show leaves and blossoms. Arriving in the camping
          area---Mary and Katarina chose the first set of flats
          beyond the big pool rather than the more extensive
          flats with (slightly) more shade. An advantage was
          that these flats gave a very good view of the big pool
          shelves so they could look for our Saturday hikers.
          Neither set of flats had trees suitable for hammock
          camping---so, I followed a cactus lined ledge to a
          climb down to the cove between the first set of flats
          and the second and set my hammock up between two
          ideally spaced box elders. Here, I had shade most of
          the time. I watched leaves being blown in and out of
          the shade and watched reflected ripples going up and
          down the redrock face and the tree trunk. The sound
          from the creek was more than a babble but less than a
          roar---very continuous and very soothing. The book I
          was trying to read kept becomming heavier and
          heavier---as did my eyelids. I slept much of the day
          as did Meg.

          I did not get my get-up-and-go back the next day. If
          the Saturday hikers had shown up I would have escorted
          them to the prettiest half mile-nearly a mile and a
          half beyond our campsite---but, we never saw them even
          though Meg constantly watched for them and I went over
          to the big pool once.

          So, we loafed in camp. Katarina was the only one who
          went swimming.

          The next day we hiked out early---while it was still

          I later learned that two of our Saturday hikers had
          come in ALMOST far enought to link with us.

          The trail in to the campsite.

















          A volcanic dike cuts through the Supai sandstone:


          Campsite area





          The climb down from the upper camping area.


          The ledge to the climb.


          Poison ivy or young box elder?????



          Meg's REI half dome. One pole too long?????


          Campers who came in at 3:30 a.m. None too quiet!!!!!!




          Yes! I paid $10 for this hammock at a Mesa surplus
          store 8 years ago!


          Other neighbors:




          Loooking downstream in the morning. Meg and Katarina
          are camped on the shelf about 15+ feet above.

        • C C Wayah
          Nice trip. How s the snow in Falgstaf? Rogene
          Message 4 of 5 , May 15, 2008
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            Nice trip.
            How's the snow in Falgstaf?
          • Blake Robert
            The snow is already gone! SOB!!!!! RB
            Message 5 of 5 , May 15, 2008
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              The snow is already gone!



              --- C C Wayah <ccwayah@...> wrote:

              > Nice trip.
              > How's the snow in Falgstaf?
              > Rogene
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