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[John Muir Trail] Re: Couple questions for June hike

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  • Robert
    Oversimplifying a bit, the down is designed to occupy the space between the bag s inner and outer diameter, and clothes inside the bag do not affect the
    Message 1 of 31 , May 15, 2013
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      "Oversimplifying a bit, the down is designed to occupy the space between the bag's inner and outer diameter, and clothes inside the bag do not affect the amount of space within which the down can "loft" "

      That space gets compressed regardless of how it's designed if you are laying on it or pressing on it with your body and too many layers of clothes on. Simply put, if you are wearing enough to press against the bag, you may be staying warm and toasty from your clothes, but you are decreasing the R-value of your bag. I have chatted with a couple of bag reps over the years on this topic, and both have told me to pick a bag that allows you to wear some type of thinner thermal clothing and have a small amount of space between you and the shell of the bag to trap warm air inside. Too big of a bag, too much airspace to warm up, too small and the down will get compressed. Another consideration to factor in is moisture in your clothing from throughout the day is not optimal for your internal bag warmth.

      --- In johnmuirtrail@yahoogroups.com, John Ladd <johnladd@...> wrote:
      >
      > On Tue, May 14, 2013 at 11:21 PM, Lauren Egert <laurenegert@...>wrote:
      >
      > > [others believe]
      > > more clothes between you and the down actually decreased the usefulness of
      > > the down
      >
      >
      > This *is* commonly believed, but I think it is mostly wrong. The inner
      > diameter of modern down bags is considerably smaller than the outer
      > diameter. Oversimplifying a bit, the down is designed to occupy the space
      > between the bag's inner and outer diameter, and clothes inside the bag do
      > not affect the amount of space within which the down can "loft". So, even
      > if you totally fill up the inside of the bag with yourself + clothes,
      > there's still room for the down. At some point, clothes in the bag are
      > overkill because they just displace trapped air which is itself insulating,
      > and overdressing gets uncomfortable, but clothing in the bag will generally
      > increase the warmth of the bag.
      >
      > Expedition-weight baselayer like Patagonia's Capilene 4 or the Army's ECWCS
      > Level 2 is particularly good inside a bag on cold nights.
      >
      > The other advantage of a lighter bag plus insulation layers of clothing,
      > when compared to a warmer bag but less clothing, is that you can wear the
      > layers of clothing when you get out of bed in the morning, though they will
      > probably come off as soon as you start hiking. Too often, if you don't
      > have enough warm clothes, you tend to stay in your bag until it starts to
      > warm up and you miss that lovely early morning hike as the sun is coming
      > up. With insulation clothing layers, you can get out of bed while it is
      > still dark and start hiking with first light and stop to cook your
      > breakfast after covering some miles.
      >
      > One important caveat to all this: If you are counting on clothing to add
      > warmth to a bag, you need similar layering for all parts of you. If you had
      > good insulation on your torso but not your legs or feet, you will be very
      > uncomfortable. So if you bring an expedition-weight baselayer top, bring
      > the pants as well.
      >
      > On the occasional sub-freezing night, wearing dry rain gear inside the bag
      > adds a surprising level of extra warmth, presumably by utilizing the vapor
      > barrier method of retaining heat. The long-distance hiking guru Andrew
      > Skurka has a good explanation, though it is mostly focused on pure vapor
      > barriers, while raingear is only a partial barrier since it allows some
      > vapor to pass through
      >
      > http://andrewskurka.com/2011/vapor-barrier-liners-theory-application/
      >
      > John Curran Ladd
      > 1616 Castro Street
      > San Francisco, CA 94114-3707
      > 415-648-9279
      >
    • Chris Pratt
      JD, I do something similar when it gets to cold for my bag. But, instead of draping the jacket over the bag I zip it up and slide it over the foot of the bag,
      Message 31 of 31 , May 15, 2013
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        JD,

        I do something similar when it gets to cold for my bag.  But, instead of draping the jacket over the bag I zip it up and slide it over the foot of the bag, like an oversized sock.  It reaches up around the knee area.  By doing this I don't have issues with the jacket sliding off the top of the bag during the night.  To me it seems that more heat is lost in the bottom part of the bag then the top. 

        Warm feet, happy sleep....

        Chris
        On 5/15/2013 11:48 AM, dittliphoto wrote:
         

        Yes, depending on how cold one sleeps, a 0° bag is overkill in the Sierra almost anytime!! 


        I've had many years of first hand experience trying to make a "light" bag work in shoulder (and winter) seasons in the Sierra. I prefer wearing long undies of some sort to keep the bag clean(er) and to avoid what I feel is a "clammy" feeling of skin against nylon.

        From my experience, wearing thickly insulated clothing (ie. down jacket) inside a sleeping bag makes other parts of your body (ie. legs and feet) colder. I attribute this to the heat from the core (torso) being trapped within the jacket and not warming the air space in the sleeping bag. 

        I have found that actually draping the down jacket outside the bag, or spreading it on top of my entire body between the bag, to be much more effective. Again, this is from several experiences over the years, your results may vary.

        JD
        Walk the Sky: Following the John Muir Trail
        see book here  
        --- In johnmuirtrail@yahoogroups.com, Lauren Egert wrote:
        >
        > My apologies for the last email I just sent! It was intended to go to a friend of mine as we were debating this very issue and the efficacy of down with lots of clothes on (she was of the opinion more clothes between you and the down actually decreased the usefulness of the down) Anyway, I'm so sorry that it got sent to all of you and not my friend!
        >
        > Lauren
        >
        >
        >
        >
        > ________________________________
        > From: Robert rnperky@...
        > To: johnmuirtrail@yahoogroups.com
        > Sent: Tuesday, May 14, 2013 10:54 AM
        > Subject: [John Muir Trail] Re: Couple questions for June hike
        >
        >
        >
        >  
        > I agree with Byron on this issue as well. A 0 degree bag is overkill for a summer hike of the JMT. Use a layering system with your clothes to increase your bags rating.
        >
        > --- In johnmuirtrail@yahoogroups.com, Byron Nevins byron.nevins@ wrote:
        > >
        > > My $0.02. I used to do that -- bring a "hot" (read: heavy) bag and sleep
        > > near naked inside. Then I came to my senses and slashed the weight of the
        > > bag (20 oz quilt) and wear clothes underneath. If cold enough -- I wear
        > > ALL of my clothes underneath. They aren't doing me any good sitting around
        > > outside of my bag. If you carry it - use it!
        > >
        >

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