[pct-l] the use of sleeping bags, design, choice, etc.

[ed faubert]

Interesting post about sleeping bags/cold butts/peeing..............
Most of you either know me or have seen photos of me and yes i could be Santa younger brother. 
I have a down sleeping bag thats a mummy one but cut pretty wide. I do a fair amount of winter canyon hiking where the temps get down to upper 20s---i have not zipped up my sleeping bag since a really cold night in 99 up by Apache Junction and never get a cold butt ! What i do have for a sleeping pad is a roll of synthetic sheep skin that i lie on at night and use my bag as a throw only, sort of like a quilt. I also rarely pitch my tent even in the winter when it gets down to freezing.  So maby it pays off to have a large butt vrs a cold butt? If i do pitch at all its a Shires floorless tarp anyway. What i am going to experiment with this month is adding a thin sheet of aluminun foil to lay down over the tyvec to see how it works
Because of not being confined inside a bag/and or a tent i just use a pee bottle which at my age is a must for cold nights.
I start a winter New Years hike 12/29 to the Colorado River in the Canyon. I stay below the rim for 10 days then come out to resupply. Then on the 11th i go back down for 8 more nights and will be joined by Billy Goat for that trip. From all indications this will be a real test of my system as its going to be really cold this time. I better eat some more choclate..........................
Meadow Ed On Sun, 12/14/08, Jim Eagleton <eagleton at hotmail.com> wrote:

From: Jim Eagleton <eagleton at hotmail.com>
Subject: Re: [pct-l] the use of sleeping bags, design, choice, etc.
To: pct-l at backcountry.net
Date: Sunday, December 14, 2008, 10:04 AM

Have any side sleepers had trouble with cold butts?  I used to be a stomach
sleeper, but have "graduated" to side sleeping for my senior bladder. 
I also got a narrow FF Hummingbird bag this year.  I know a differential cut is
suppose to keep the down from compressing, but I have had someone problems this
year.  It's hard to do a side by side comparison with the standard cut mummy
bag.  
Rambler
 
> From: elee at microsoft.com> To: ned at pacificcrestcustombuilders.com;
peprmintpati88 at yahoo.com; pct-l at backcountry.net; paul_c at tuxcnc.org> Date:
Fri, 12 Dec 2008 12:28:32 -0800> CC: public at postholer.com> Subject: Re:
[pct-l] the use of sleeping bags, design, choice, etc.> > Mtnned
wrote:> >> The body radiates heat into the space between the skin and
the down and> eventually it is held by (or bonds onto) the fine fibers of the
down quills.> The down holds it undisturbed better than does the space
between the skin> and the down, thus, allowing the heat to be held in the
down is more> efficient. The closer the down can be to your skin, the less
energy the body> has to expend on heating the space between.> >>
> Thanks, Ned! I certainly don't have anywhere near your experience with
outdoor skills or gear design, and I'm a software developer, not a
physicist, but I want to point out a couple small corrections in terminology
that might help people to reason about this stuff in a more a
 ccurate way, and maybe get better at solving problems in the field.> >
First, insulation of any type doesn't hold or soak up heat, at least, not if
it's any good. Insulation is not a heat *sponge*, it's a heat *barrier*.
It doesn't keep you warm by soaking up heat and then giving it back to you
later. It works by not letting heat leave the area you're trying to keep
warm (in this case, your body). Insulation only works precisely because it
doesn't transfer much heat into or through itself, or at least does so very
slowly.> > Imagine that you put a block of metal and a bag of down in a
freezer and leave them there for a week. Then you take them out and hold one in
each hand. The hand with the metal block will get really cold really fast
because metal is a heat sponge; heat flows into it easily and it can absorb a
large quantity of heat. The hand holding the down may get somewhat cool
momentarily, but it'll warm right back up again. That's because the down
is a heat barrier; h
 eat doesn't flow into it easily and it doesn't absorb much heat. Your
hand feels warm even though the bag of down itself will still be below freezing
in the middle.> > The other correction is that heat doesn't magically
disappear, and objects don't consume heat merely by existing. Once something
is warm, it stays warm forever unless the heat is allowed to travel somewhere
else. Heating up the air between your skin and the bag is a factor when you
first climb in, of course, but once it's warm it stays warm except for heat
leaking out through your insulation. I've heard people suggest that you
should make sure to pee before sleeping because that way your body doesn't
have to waste heat keeping that urine warm. That doesn't make any sense.>
> Here's another thought experiment - imagine that you're trying to
fill up one of those big plastic swimming pools you can buy for your back yard.
The goal is to get the water deep enough for you to swim in. But you have two
problems; one, 
 the walls of your swimming pool leak. Two, the hose you're using to fill
it isn't very big and supplies only a trickle of water.> > There are
three ways to solve your problem. One, you could get a bigger hose. As long as
you have more water coming in than is going out, you'll be able to fill the
pool. Two, you could fix the leaks in your swimming pool walls so that they lose
less water. Or three, you could get a smaller pool. Even if the walls of the
smaller pool are made of the same leaky material as the larger pool, it will
leak less water overall because there's less leaky wall area so your hose
can keep up.> > In any case, the water in your pool doesn't magically
disappear on its own. You wouldn't say, oh, I need to get rid of this bucket
that's submerged in the pool because otherwise my hose will have to
constantly spend water to fill up the bucket over and over again. Once the
bucket is full, it's full. It's no longer a factor in the overall
equation of water coming in
  and water going out. The only things that matter in the long run are the
input source and the barrier.> > Eric>
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