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

[ned at pacificcrestcustombuilders.com]

Thanks, Eric! I always appreciate your insights.

After 34 years of teaching wilderness travel skills, selling the gear, even 
designing some, but mostly testing new, sponsored gear on our school trips 
(Mountain Education) as well as the longer voyages on the pct and cdt, I'd 
like to encapsulate what has been said in the light of all this:

The premise of clothing is to capture body-radiated heat next to the skin 
and thereby keep us warm. The more air that can be held within the fibers 
(micro fibers), the greater the R-value, so to speak, of the garment. Thus, 
a down jacket, which, efficiently, can hold a lot of air heated by the body, 
has the potential of keeping you very warm-as long as the wind doesn't blow 
it out of the spaces held by the fine feathers. Therefore, the need, in a 
windy and cold environment, for a wind-proof outer covering over the down 
jacket. The thicker the garment (full of fine fibers), the more air it can 
hold, the better the insulator. Same with home insulation.

Now, a sleeping bag was designed to work the same way. Heat held still, as 
Eric said, within the clothing, will keep you warm. But, when clothing is 
worn inside a sleeping bag, it prevents the heat from being held more 
efficiently within the down and you are warmer because of the multiple 
layers involved, not because you have the most efficient bag.

Mountain Hardwear, The North Face, Sierra Designs, and Marmot all sponsored 
me in one way or another over the years or taught me how to sell their 
clothing and the gist of the sleeping bag design was this:

    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. A tight bag is more efficient, 
but don't plan on rolling around in it. Roll around with it! Movement does 
encourage or push heated air out of the bag, so the process of reheating 
begins all over again, roll after roll, all night long.

    Here is where membranes come in which reduce cold air from blowing the 
heated air out and keep you from rolling the air out as well. They are 
marketed with many names, but they work wonderfully and greatly increase the 
rating and efficiency of the bag (price tag, too).

    Hoods, draft collars, zipper draft barriers, foot boxes, half zippers, 
etc. all contribute to keeping the heat in and a more efficient bag.

    The bigger and finer the feathers, the more heat can be held. The more 
the down is crushed, stuffed, stored stuffed, the less the feathers can 
expand and hold air. Uncertain about how dirt and body oils contribute to 
efficiency loss. With use, the feathers will crush and the bag will loft and 
hold heat less. They have a lifetime.

    Store down as un-stuffed as possible. Hanging on a sleeping bag hanger, 
open under the bed, in a storage stuff sac (laundry bag as mentioned), for 
reasons above.

The only way to decide what kind of bag works best for you is to try out 
different types (down vs. synthetic), sizes (mummy, rectangular, quilt...), 
designs (slanted baffles, chevron slanted baffles, longitudinal baffles, 
quilts sewn-through, etc.), loft heights, and on and on.

For the most part, men create more heat than women. Therefore, we have 
always encouraged the ladies on our trips to choose down articles (parkas, 
booties, bags...) unless allergic, then go with the synthetic.

Most of all, Know Thyself. Only you can know what works best for you in the 
conditions you expect to encounter. To find that out, take numerous pre-trip 
weekend test hikes in all the worst weather and terrain. Just because it 
seems that most folks do the pct in an "ultra-light" manner and take a tarp 
or no stove doesn't mean you will want to or should. Part of wilderness 
hiking is discovering who you are and what matters to you, apart from the 
maddening crowd. Go work out the details as they pertain to you, then go 
hike the Crest!

Mtnned
----- Original Message ----- 
From: "Eric Lee (GAMES)" <elee at microsoft.com>
To: <peprmintpati88 at yahoo.com>; <pct-l at backcountry.net>; "Paul" 
<paul_c at tuxcnc.org>
Sent: Thursday, December 11, 2008 12:40 PM
Subject: Re: [pct-l] Sleeping Bag Ratings


> Patti wrote:
>>
> actually the more layers u wear the colder u are from what I was told b/c 
> the bag uses ur body heat to warm up. So if ur wearing more layers then 
> it's that much more work for the heat to get to ur bag...just what I was 
> told by several bag reps that's all
>>
>
> I'm pretty sure that's nonsense, no offense.  The idea here is to keep the 
> heat from leaving your body.  It doesn't matter what kind of insulation 
> you use to accomplish that, or what temperature the bag itself is.  The 
> more clothes you wear, the more total insulation you have and the less 
> heat escapes.
>
> Now, there are a few important caveats that I suspect people get mixed up 
> with the main idea, resulting in the advice you got from the bag reps.
>
> The first is that you don't want to wear really tight clothes, or so many 
> layers of clothes that they become tight.  If you do, that will restrict 
> blood flow to parts of your body and those parts will end up feeling cold.
>
> Second, you don't want to wear damp clothes to bed, because as the 
> moisture evaporates off of them it takes your heat with it.  If all you 
> have are wet clothes, you may be better off wearing no clothes at all. 
> But dry clothes are always better than no clothes.
>
> The third is that you don't want you plus your clothes to be too big for 
> the bag, which compresses the bag's insulation.  Sometimes people think 
> that it's the actual feathers or synthetic fibers themselves that trap 
> heat, but it's actually the still air trapped inside the insulation that 
> traps the heat.  If you compress the insulation, there's less trapped air 
> and so it works less effectively.
>
> Fourth, you don't want a bag that's too big for your body, not because it 
> takes more work to "heat up" a big bag, but because a big bag has more 
> surface area.  Assuming your bag is relatively uniform, each square inch 
> of your bag will leak a certain amount of heat based on the relative 
> difference in temperature between the inside and the outside.  If you add 
> more square inches of surface area, that's more total heat that's leaking 
> out.  If you reduce the surface area, that's less heat that's leaking out. 
> At least, until you hit the third caveat above.
>
> Eric
>
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