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#106593 - 11/17/08 04:19 PM Clothing Science and Folklore - open discussion
JAK Offline
member

Registered: 03/19/04
Posts: 2569
I thought I would put this in Lite Philosophies and Practices to keep it generic. It's intended to be about stuff like how to figure out how much clothing and sleeping material you need, both in theory and in practice, and how much it weighs. Looking for diversity of opinion here. Science old and new. Folk-lore old and new. Even marketing hype is welcome. It's not intended to be comprehensive or compete with sound established theory and practice. It's to stretch and broaden our understanding of it and have some fun discussion and share some interesting links, both the useful and the arcane.

Here are some related links:

Wikipedia article on layered clothing...
http://en.wikipedia.org/wiki/Layered_clothing

Interesting old article on antarctic clothing...
http://dspace.ncaor.org:8080/dspace/bitstream/123456789/291/3/article31.pdf

Very interesting new book that discusses thermal regulation...
http://books.google.com/books?id=_hHp5ov...p;amp;ct=result

Thread drift is encouraged. <img src="/forums/images/graemlins/smile.gif" alt="" />

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#106594 - 11/17/08 05:36 PM Re: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Wicking - Why is Wool warm and Cotton cool?

I gained some new insight the other day. I think it was from that hot brain book. We understand that wool can hold 35% of its weight in moisture before it feels wet, but why does it sometimes 'feel' warm, even warmer than fleece or down? Also, what's up with the base layer? Is is just a wick, or is it more?

First, why is wool warm?

It turns out that even when we are wearing the right amount of cool weather clothing so that we are not sweating our body is still giving off moisture. This moisture evaporates from our skin, which takes heat in the form of latent heat of vapourization. Water vapour doesn't need to be 212degF. It can exist as partial pressure at cooler temperatures. The skin surface is about 85degF when wearing a comfortable amount of clothing. This latent heat comes from the sensible heat of the skin and the moisture it is giving off. If we are wearing a wool sweater or wool mitts or wool socks this water vapour re-condenses as it passes through the the wool, because it cooler than the body the further you go out. This condensing releases the latent heat, which makes the wool warmer than it otherwise would have been. So the wool gains both latent heat and sensible heat from the moisture. If you are wearing wool mitts and you get a gust of wind your hands will first feel cool as more moisture evaporates off the skin, but then they will feel warm again as they gain some heat coming back from the wool. The wool doesn't produce any heat, everything it gains from the body must eventually be released to the environment, but it acts like a thermal capacitor, absorbing and releasing both latent and sensible heat. There is also some additional heat released when moisture freezes on the outside of your clothing, and the heat is taken up when the ice melts or sublimates, unless you brush the ice crystals off now and then. Fur is particulary good at managing this heat of fusion, by allowing ice crystals to be shed.

Why is cotton cool?

Cotton can also absorb water, and thus can store both latent and sensible heat the same as wool. The difference is that wool still acts as both insulator and thermal capacitor when it is wet, whereas the cotton is more likely to be saturated, which effectively short circuits heat directly away from the body, and so the body loses heat as though it were naked and soaking wet, even colder because they can effectively increase the surface area for evaporation while providing a negligible amount of insulation.

What about polyester, silk, cotton flannel, etc?
Depending on how they are put together, most insulating materials, even cotton, can provided varying degrees of thermal insulation and thermal capacitance before short circuiting. In hot weather you want something more like thin cotton. In cold weather you want behaviour more like wool, but the total amount of capacity for holding moisture without short-circuiting varies depending on the climate and application. Wool itself varies in its porperties. Some wool is better for very wet and cold weather. Some wool is more like down, not as good in wet weather but lighter for its warmth in dry weather.

So what's up with base layers?

So a base layer can have many functions.
1. Thermal insulation against thermal conduction.
2. Thermal capacitor of both latent and sensible heat.
3. Allowing transport of both water vapour and liquid moisture.
4. Providing increased surface area for both evaporation and condensing.
5. Short-circuiting its thermal insulation when saturated, for hot weather.
6. Or retaining some thermal insulation when near saturated, for cold wet weather.

I am still not entirely sure of the distinction between base layer and mid-layer, or whether skin fitting base-layers are always needed for comfort. Genrally speaking on a long trip you only need to optimized performance for the worst possible conditions. The rest of the time is largely a matter of comfort and convenience. Most of the time I just wear a wool sweater without any skin layer underneath or shell layer over it, but I have those extra layers in the pack to switch it into a parka or foul weather jacket.

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#106595 - 11/17/08 05:40 PM Re: Clothing Science and Folklore - open discussion [Re: JAK]
verber Offline
member

Registered: 01/26/04
Posts: 269
Loc: SF Bay Area, CA
Over the last few years I have created a recommended outdoor clothing page where I tried to capture everything I have learn about clothing as well as links to other people's materials.

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#106596 - 11/17/08 06:06 PM Re: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
What is a clo, and how much does it really weigh?

1 tog is 0.1 m2K/W.
It is a measure of thermal insulation per unit area. 2 square meters of clothing with a value of 10 togs will lose heat at a rate of 100 watts when the outside temperature is 50degC below skin temperature.

1 clo = 1.55 togs, which is that of a 'standard british business suit'.

How much does it really need to weigh?

You hear this quoted alot. "10 pound of clothing = 1.5 clo". Rubbish. That is only true if you insist on backpacking in 1.5 standard british business suits.

How about a medium wool sweater and 200wt fleece pants, each with a light nylon shell over it, and maybe a light skin layer underneath? And how about some hats and mitts and thicker socks, and turn in the oxford shoes for trail runner?

Perhaps 2.5 pounds in total, not counting the shell or trail runners.
The shell is neccessary to get the full clo, but I would add that weight extra.

But what's the clo or tog value?

According to this article, see the last page...
http://dspace.ncaor.org:8080/dspace/bitstream/123456789/291/3/article31.pdf

Dead air has a value of 2.9 togs/cm, and clothing insulation achieves a value of about 2.44 togs/cm. That works out to about 1.5 clo per cm thickness, or 4 clo per inch. I would guess that you might get about 1/2" of loft from the above described outfit, of about 2.5 togs. So a good rule of thumb for an adult is a clothing insulation weight of 1 pound per Tog to cover the entire body of a large adult hiker, plus the weight of your shell and boots. This assumes very even coverage including head, hands, and feet, and your insulation is loose and not overly dense or compressed.

1 pounds of full body clothing insulation = 1 tog.
So for 1/2" of clothing loft for 4 togs of winter clothing you would need 4 pounds of wool, fleece, and base layers, plus another 2 pounds for shell layers and footwear. For 8 togs you would need 8 pounds plus 2 pounds for 10 pounds, or perhaps some of that extra 4 togs could be down, which might be 2 togs per pound including its own shell layers. In summer you might only need 1 tog but it might weigh 2 pounds because of thin and uneven coverage, plus you still need another 2 pounds for shell and footwear.

Total clothing weight as a function of minimum temperature?
This is just a guess now...
50F = 1 pounds + shell and footwear = 3 pounds, maybe less but who cares its so little.
30F = 2 pounds + shell and footwear = 4 pounds, but can be very wet also at 30F ???
10F = 3 pounds + shell and footwear = 5 pounds
-10F = 4 pounds + shell and footwear = 6 pounds
-30F = 5 pounds + shell and footwear = 7 pounds

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#106597 - 11/17/08 07:56 PM Re: Clothing Science and Folklore [Re: verber]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Quote:
Over the last few years I have created a recommended outdoor clothing page where I tried to capture everything I have learn about clothing as well as links to other people's materials.
That's a great article. I am surprised that for light work loft is 0.8 inches at 40degF, but I see that is for torso. Perhaps it can be less for even coverage. In winter at 40F doing light duty I tend to be unevenly covered, unless its windy, because I am saving some other layers for colder temperatures and so I might undress unevenly, like medium sweater and hiking shorts. In summer when its 40F doing light duty it probably after dark and I am likely to have all my layers on except my rain layer, so it would be fairly evenly distributed, and likely less than 0.8 inches, perhaps 0.4 inches, like a skin layer and thin merino sweater and wind jacket. Of course even a light merino sweater and wind layer can puff up a bit, but that's hard to measure until you get reasonably thick, as in winter.

Any good tables on total clothing weight as a function of minimum expected temperature. Tricky thing is that minimum expected temperature in summer tends to be wet, whereas the minimum expected temperature in winter tends to be dry, at least if the minimum expected temperature is well below freezing. It might be best to add an extra pound if the minimum expected temperature is above 20F, but then you might need to add an extra pound below 20F also for other reasons, like the body's heat storage reserve is relatively less, so you might need that extra just to warm back up after doing something.

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#106598 - 11/17/08 08:09 PM Re: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
I found this link in your link...
http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

Very nice chart on clo vs temperature and activity. It's based on the skin temperature of 85F. I see where you might have come up with 0.8" of clothing loft for light activity at 40F. That's a bit sketchy because it includes the surface effect, which sort of comes with the shell layer but can only be counted once and is reduced by wind chill effects. But it is a very practical chart in a way as it provides some extra allowance for the wetter conditions you often get from 20F to 40F.

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#106599 - 11/17/08 08:45 PM Re: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Clo per ounce...

I don't agree with this table. It is very misleading.

clo/oz
Cotton 0.04
Merino wool 0.08
Polartec 100,200, 300 0.16
Polarguard 3D 0.63
Exceloft 0.68
Polarguard Delta 0.68
Climashield HL 0.68
Down (550 fill) 0.7
Primaloft Sport 0.74
Climashield Combat 0.79
Climashield XP 0.82
Primaloft One 0.84
Down (850+ fill) 2.53

It shows merino wool at 0.08 clo/oz and Down at 2.53 clo/oz. You certainly won't save 30 pounds of wool with a 1 pound down jacket. You might save 1 pound on a total clothing system of 5 pounds vs 4 pounds, for the same warmth in dry cold, but the 2 pound wool sweater would better for the cold wet freezing rain.

All winter clothing systems are about 4 clo or 6 togs per inch. A full inch of loft is a pretty heavy duty winter system, perhaps 6 pounds not counting your shells and footwear. Your not going to shave off much of that by using down until you go well beyond 6 togs. You might save 0.5 pounds for every additional tog beyond 4 togs. Not sure. But how many togs do you really need?
7-8 pounds including footwear and shells for 6 togs is already alot of clothes, and I think down only saves a pound tere.

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#106600 - 11/17/08 10:40 PM Re: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Interesting article on wool/silk/wool/silk layering system.

http://www.outdoorsmagic.com/news/article/mps/UAN/3517/v/1/

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#106601 - 11/17/08 11:25 PM Very little advance in "clothing science" [Re: JAK]
johndavid Offline
member

Registered: 04/23/08
Posts: 260
Loc: jersey city NJ
Myth that contemporary clothing is better than 1920s.

The improvements have indeed been minimal (except for boots I'd guess)

Recent research on Mallory's clothing:

"Their layers of wool, silk and cotton was lighter than modern clothing and extremely comfortable to wear
Mallory’s boot was the lightest ever used on Everest
The 1924 Everesters were lightweight specialists who understood their clothing better than most modern climbers
The complete set of garments was field tested on Everest, by Graham Hoyland, the great nephew of Howard Somervell, in April 2006. He confirmed that the replicated garments indeed formed a sophisticated, effective and comfortable clothing system which ‘was perfectly adequate for a summit bid’. Graham Hoyland , Everest, April 2006 "

see

http://www.innovation-for-extremes.org/mallory_myths.html#gear

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#106602 - 11/18/08 03:03 AM Re: Very little advance in "clothing science" [Re: johndavid]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Perhaps the ideas of modern vs primitive clothing systems for cold weather could be introduced.

There was a PBS program on the sailing technology of the Viking era Scandanavians a few years ago. They gave attention to the ships and the clothing.

They recreated the clothing and compared performance of this to modern cold weather sailing clothing with high tech fabrics. It was found that the ancient clothing designs performed well in comparison.

In addition, there are the stories of polar explorers who took the time to study the Inuit indians living in the polar areas. Some aspects of these cold living peoples were put to good use in the initial successful expeditions to the South Pole.

Us "moderns" tend to ignore much of history. Sometimes, to our great loss.

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#106603 - 11/18/08 03:18 AM Re: Clothing Science and Folklore [Re: JAK]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Quote:
Wicking - Why is Wool warm and Cotton cool?

<trim>

Why is cotton cool?

Cotton can also absorb water, and thus can store both latent and sensible heat the same as wool. The difference is that wool still acts as both insulator and thermal capacitor when it is wet, whereas the cotton is more likely to be saturated, which effectively short circuits heat directly away from the body, and so the body loses heat as though it were naked and soaking wet, even colder because they can effectively increase the surface area for evaporation while providing a negligible amount of insulation.

<TRIM>


.


Cotton is cellulose and it is microscopically present as thin walled hollow tubes. Water will evidently "plasticize" the cellulose and allow the collapse of the thin walled hollow tubes. This geometry change would exhibit a strong effect on the thermal conductivity.

It is said that this accounts for the visual aspects of the "Wet Tshirt" effect which elicits whistles and shouts.

A thoroughly wet Tshirt would allow a continuous path of water to act as a high conductivity path acting in parallel with whatever insulation capabilities collapsed thin walled cellulose tubes exhibit. In effect, this could act as a thermal conduction "short circuit".

Really wet wool would also exhibit the same "short circuit", but people commonly claim that if wool gets drenched, wringing it out and putting it back on the body quickly results in a drier and warmer situation. This could also work the same way for synthetic fabrics.

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#106604 - 11/18/08 05:57 AM Re: Very little advance in "clothing science" [Re: Roocketman]
Pika Online   content
member

Registered: 12/08/05
Posts: 1726
Loc: Rural Southeast Arizona
Quote:
in addition, there are the stories of polar explorers who took the time to study the Inuit indians living in the polar areas. Some aspects of these cold living peoples were put to good use in the initial successful expeditions to the South Pole.


Having spent six months in the field in Antarctica, having read a lot about the early expeditions and having seen their gear in their abandoned housing , I agree that the early explorers were knowledgeable about clothing and equipment available at the time and that they did use a lot ol Eskimo technology.. But, I do not agree that their gear was just as good as that available today.

Remember that Scott and all of his party died on his return from the pole. One of the problems the Scott polar party had was heavy and somewhat ineffective gear. Their equipment had to be laboriously man-hauled on sleds. Exhaustion and not having enough food was a major problem.

Scott and Shackleton both equipped their expeditions with Inuit equipment. They used reindeer hide sleeping bags, they used a grass that grows in Greenland to provide insulation in their boots and used heavy sealskin parkas and pants for outer wear. Ammundsen seemed a bit better prepared. IIRC, he used fabric and wool rather than hides and he made it back from the pole.

Reading accounts of some of their explorations (The Worst Journey in the World by Apsley Cherry-Gerrad), you come across commentary on how badly the reindeer bags shed hair that then got into everything including their food. And, as the bags shed, they got colder so they lost sleep. The grass they used to line their footwear would pack down and loose its insulation value and needed to be replaced fairly often. The sealskin clothing worked well but was heavy and not particularly comfortable. I remember reading several comments on how stiff it would get if it got wet.

The clothing and sleeping bag that I used about 60 years later were comfortable, warm and didn't shed into my oatmeal. It was still heavy by BPL standards but it was bombproof in conditions that put a premium on durability.
_________________________
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#106605 - 11/18/08 09:20 AM Re: Very little advance in "clothing science" [Re: Pika]
johndavid Offline
member

Registered: 04/23/08
Posts: 260
Loc: jersey city NJ

Scott suffered terribly from the cold on what was supposed to be a 1,700-mile hike, but came up short due to a lack of food and water.

My point is, there is a degree of hype out there about "modern advances."

Horace Kephart in about 1914, listed three separate camping outfits from England sold as kits that each weighed about six pounds and included tent, sleeping and cooking gear, along with a small stove and other odds and ends.

I'm sure the stuff was entirely functional. So the notion, for example, that today we have lighter equipment is essentially false.

Today's alcohol stove and aluminium cooking gear is nearly unchanged from at least 1918. Same with sleeping bags. The other stuff has surely gotten a bit better.

I'm not going to give up nylon fabric nor shop in vintage boutiques, but my guess is that there is even less functional differences in the wardrobe department than in camping gear.

I especially do, however, prefer the newer footwear to leather-soled boots with tricouni nails.

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#106606 - 11/18/08 05:35 PM Re: Very little advance in "clothing science" [Re: johndavid]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
I could be wrong but I think even if they had modern down sleeping bags back then they would still have a problem with them icing up. The big advantage today I think is that they can airdrop fuel to heat a place up very warm in order to dry stuff out. Just heating up a tent isn't enough when its really cold. Just makes it humid. You really need a camp to dry stuff out otherwise your just melting the ice and freezing it again, plus some. I read someplace that bags can gain 50g a day of ice in polar conditions, which is almost a pound a week. It was only one article though.

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#106607 - 11/18/08 06:16 PM Re: Very little advance in "clothing science" [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Where do you hang your clothes from, while they are on you that is.

I wish there was a better selection of how high the waist is on bottoms and how low the hemline is on tops. If you were to design you own layers, how would they overlap, and where would they all hang from. Not to critical for light winter clothing, but for heavier layers it requires a little more though. Bottoms with an elastic waist in the wrong place can be a drag. Bibs and suspenders and long johns have their place, as do long coats.

Here is just one idea. I have some of this stuff. This would be for a long mid-winter trudge, down to -20F, -30F maybe, but also alot of wet stuff between +20F and +35F, always with the chance of rain, which is a real bugger with snow.

40 oz bottom
Skin layer bottoms = Bottom half of merino wool long johns combis 14oz
Mid layer bottoms = Silk bottom with high waist = 6oz
Extra layer bottoms = 200 wt fleece = 12 oz
Shell Layer bottoms = brushed nylon hiking pants, bloused = 8oz

50 oz top
Skin layer top = Top half of merino wool long johns combis = 14 oz
Mid layer top = Light Shetland Wool Sweater to just below waist = 20 oz
Extra layer top = 100 wt fleece to just below bum. = 10 oz
Shell layer top = Light breathable nylon to just below bum. = 6oz with hood

Plus wool socks, wool mitts, wool neck tube, wool hat with ear flaps, brimmed hat. For clarity I haven't gone into neck and wrist and ankle issues, just waist issues. 22 oz total maybe. Not sure, but that would make for a total of 7 pounds, plus footwear and rain poncho/tarp or rain bivy/cape or whatever.

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#106608 - 11/18/08 06:27 PM Re: Very little advance in "clothing science" [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
I rediscovered blousing tonight?

I remeber we used to have to blouse the bottoms of our combat pants with these little stretchy bands with hooks. It's a pretty cool idea really. Anyhow I have these light brushed nylon hiking pants which have zip bottoms with a little bit of flair for boots, and the are quite long and breezy, which is a waist of material. So I folded them up inside, with an elastic on the inside which blouses it against my calf. I can adjust the height, depending on socks, and the blousing makes the pants a bit puffier which traps alot more air than simply tucking them into my socks.

Got to thinking that this sort of blousing might be good on other layers, like sleeves and hem of my wind jacket. I have an XXL light nylon and it is oversized enough that I can blouse it some, rather than just stretch it down as far as I can. I think this is a good way to get the most out of fleece and wool layers. Some waist bands can be a real bummer though. Needs more work to get things hanging right.

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#106609 - 11/28/08 04:22 AM RE: Clothing Science and Folklore [Re: JAK]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Some of you may have read this paper by Paul Siple. It's a bit of a classic. Let's see if this link works. You might not have access to it unless your at a university or someplace. I might be able to email the *.pdf if anyone was interested.

http://www.jstor.org/stable/985325?&...ice=showArticle

Here are the contents...

Introduction
The human body as a heat-producing machine
The major source of heat production
Minor causes affecting heat production
How the body releases or conserves its heat
The cooling demand of the atmosphere
Clothing as an insulator of body heat
Practical formulae for computation of clothing insulation
Principles for keeping the body warm
Protection against cooling by moving air
Protection against vaporization
Three methods of dressing
Cold-climate underwear requirements
Outer clothing requirements
Principles for keeping the hands warm
Principles for keeping the feet warm
Principles for keeping the head warm
Summary
Bibliography


It is very readable, and both objective and practical. What I found most interesting was the effects of solar insolation, and the effects of the storage capacity and insulating ability of the outer 1-3cm of skin when in the vasoconstricted state, also the difference betweeen feeling cold and actually being cold. That helps explain in more quantifies terms why we can wear very little walking to the bus stop and even waiting for the bus, even for an hour, but how the cold will eventually catch up to us and overcome us unless we insulate ourselves better and/or produce more heat. Similarly, wool has a great capacity to feel warmer as it slowly absorbs water vapor, but it will eventually needs to be dried out, rather like recharging a thermal battery.

I would like to study more about how wool absorbs moisture, (up to 35% of its bone dry weight without feeling wet), and how quickly and effectively it can be dried out now and then, either by fire, or solar insolation, or body heat, and perhaps dry wind. Also wondering when freeze drying at night might be effective.

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#106610 - 11/28/08 12:30 PM Re: Clothing Science and Folklore - open discussion [Re: JAK]
pennys Offline


Registered: 12/31/01
Posts: 2842
Loc: Washington
Quote:

Thread drift is encouraged. <img src="/forums/images/graemlins/smile.gif" alt="" />


My favorite bit of folklore and mistruth;

NOT washing stuff is GOOD for it.
You will ruin it by washing it.

This applies to wool and goretex. I have had people refuse to send me things (clothing)to fix when they haven't washed it for 15 years and I tell them I won't touch it unless they wash it.

( I will not go into my annual what is wrong with people who send me dirty clothing rant) <img src="/forums/images/graemlins/tongue.gif" alt="" />
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#106611 - 11/28/08 02:00 PM Re: Clothing Science and Folklore - open discussio [Re: pennys]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada
Quote:

My favorite bit of folklore and mistruth;

NOT washing stuff is GOOD for it.
You will ruin it by washing it.


Smirk.. reminds me of conversation with my wife about my much loved wind shirt.

"But if I wash it I'll have to re-nikwax it! and it'll look clean! and it won't smell like nasty hiker funk!"

At least I managed to catch her complaining about me buying a bottle of nikwax at MEC and therefore got to ask her if she'd rather I didn't wash my gear.. I now no longer require CFO permission to buy nikwax <img src="/forums/images/graemlins/smile.gif" alt="" />
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My 3 season gear list
Winter list.
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#106612 - 11/28/08 03:51 PM Re: Clothing Science and Folklore - open discussio [Re: phat]
pennys Offline


Registered: 12/31/01
Posts: 2842
Loc: Washington
nasty hiker funk is just fine for personal use, just don't send it to me to work on. <img src="/forums/images/graemlins/grin.gif" alt="" />
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#106613 - 11/28/08 05:24 PM Re: RE: Clothing Science and Folklore [Re: JAK]
Folkalist Offline
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Registered: 03/17/07
Posts: 374
Loc: Fredericksburg, VA
JAK, as you thought, you need to have membership or be at a university or other institution. It sounds like a great article. I will PM you my email if you are still able to send it.
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#106614 - 11/29/08 10:40 AM Re: Clothing Science and Folklore - open discussion [Re: JAK]
Paul Offline
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Registered: 09/30/02
Posts: 778
Loc: California
This may or may not be thread drift:
Two things I try to keep in mind if someone aks me to recommend appropriate clothing for a particular place and season (say the Sierra nevada, above 11,000 feet, April) are that different folks can vary a lot in the amount of insulation they need, and one person can vary in the amount of insulation they need from one trip to another. You can even have two people who are opposites in insulation needs depending on whether they are moving or sitting around. I have a ski buddy who I've been on numerous backcountry ski trips with. When we are moving, I need significantly less insulation than he does - I'll be skiing in just my long johns while he has shell pants over his long johns and a light windshirt on top. But in camp, he can wear less than I do and still be comfortable.
And I've had the experience of needing differnet amounts of insulation in what seem to be the same conditions. The most common version of this is that if I get really tired, I definitely need more clothing to stay warm or to sleep warm. Also, if I don't eat well I'm not as warm. I notice this most on the first night of a trip at altitude. Usually my appetite is low when the first night is at 11,000 feet or so, and I definitely don't sleep as warm that first night.
So, I am conservative in suggesting what will work for anyone else, knowing that they may have very differnt requirements than I do. And I would warn anyone that you shouldn't assume that you've got your clothing system down to a science until it has worked for you over the course of several trips in similar conditions.

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#106615 - 11/29/08 01:23 PM Re: Clothing Science and Folklore - open discussion [Re: Paul]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
Interesting observations Paul. That article,( sent to Folkalist <img src="/forums/images/graemlins/wink.gif" alt="" /> ) sheds some light. You can go a few hours quite underdressed, because as you vasoconstrict your outer 1" of flesh slowly gives up heat, making up for the deficit, plus the skin itself starts to act as an insulator. Eventually however, you gotta put more clothes on or increase your activity level. People can acclimatize in being able to tolerate colder skin temperatures, thereby utilizing the outer 1" of flesh as insulation. He says however that bodyfat doesn't play a huge role in insulation value because it isn't distributed evenly enough like blubber on a walrus. I think it must help some though. It might not prevent frostbite, but it certainly adds some insulation in some places.

The practical heat storage of the body is about 100kcal, which while sitting in camp could allow you to lose 150kcal/hr for 2 hours while only generating 100kcal/hr. The insulation value of human skin can be 1 or 2 clo. Wool can also act to generate some heat by capturing the 20kcal per hour released to the wool as water vapour. This effectively increases its r-value by 20%, but the effect only lasts until it gains 35% of its weight in moisture, and then it needs to be effectively 'recharged' by losing moisture somehow, either by an increase in body heat, or solar insolation, or from a fire. It can absorb more than that, but the effect starts to become negated by an increase in thermal conductivity, rather like internal shorts in a battery. A dangerous corolary to all that is that by utilizing the temporary boost from cold climate acclimatization and falling skin temperatures and from wools vapour heat recovery you can get lulled into a false sense of security. Clothing tests really need to last 24 hours or more, not just 2-4 hours. Something to bear in mind. Another good rule is to maybe skimp on clothing, or on your sleeping bag, but never both.

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#106616 - 11/29/08 02:02 PM Re: Clothing Science and Folklore - open discussion [Re: JAK]
Folkalist Offline
member

Registered: 03/17/07
Posts: 374
Loc: Fredericksburg, VA
Thanks, Jamie! So far it is very readable. <img src="/forums/images/graemlins/smile.gif" alt="" />
_________________________
Why am I online instead of hiking?

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#106617 - 12/08/08 06:31 AM Re: Clothing Science and Folklore - open discussion [Re: Folkalist]
JAK Offline
member

Registered: 03/19/04
Posts: 2569
1. How cold can you sleep comfortably naked? I mean without the sleeping bag or any covers. Apparently you can get aclimatized to it. I'm not sure what the practical value is in this except to get to know more about heat loss from the human body and skin temperature. It would depend on such things as air temperature, humidity, rain, raidant heat loss or gain from surrounding object, and what surface you are sleeping on. Let's say there is a tarp overhead, or you are in your living room. I've tried this at home and found that you have to give yourself some time to get used to the cooler skin temperature, but I have a feeling it might actually be healthy.

2. How cold can you sleep naked except for an 8oz ground pad, a 20oz wool blanket, and a 4oz nylon shell? Let's say there is a tarp overhead.

3. How cold can you sleep naked except for an 8oz ground pad, a 20oz wool blanket, a 4oz nylon shell, plus lets say 16oz of summer clothing, like a merino sweater and 100wt fleece pants, socks, fleece gloves and hat? Let's say again there is a tarp overhead.

I think once we get to #3 you might be able to get down to 40F and still get a comfortable nights sleep. Depends on some factors like still air, and whether we are talking about the general outside temperature or the temperature in the microclimate you have chosen for yourself under a tree on a hillside versus a rocky beach exposed to the night sky. It is easy to get mislead however, and as you get acclimatized to sleeping colder you might actually be closer to trouble. Some folks might think they crank out more heat while sleeping, and they might be right to some small degree but there are likely other factors at play. For example, wool can absorb moisture slowly, the moisture your body gives off even when you are sleeping and not sweating, and feel warmer that way. So it is about 10% warmer than its r-value alone, but only as it is gaining this moisture. It would have to be dried out before the next night, It can gain 35% of its weight without feeling wet, so the 20oz of wool might weigh 18oz when bone dry, and 24oz when it contains 35% moisture but still feels dry, not damp. Another factor is that your outer layer of skin can gradually drop in temperature from the time you go to bed and the time you wake up, and you can be acclimatized to tolerate lower skin temperatures and still sleep soundly, so even if you are only generating 80kcal per hour you can lose heat at a rate of perhaps 120kcal per hour over 6 hours before you wake up and need to warm yourself up. Of the 40kcal/hour deficit, 15kcal/hour might be made up capturing the moisture in your wool blanket, and 25kcal/hour might be made up by the heat lost from your skin, and it might be 6 or even 8 hours before you need to do something about that. The thing is this isn't hypothermia as your rectal temperature might still be fine, but you would be closer to hypothermia when you do wake up, as you have used up some of your natural built in safety blanket, like what allows you to nip out to pee in the middle of a frosty night.

I guess my point is that it is easy to get a false sense of security after some practice and a 6 hour test in the backyard, but there is a difference between being conditioned, and being safe in real conditions. Always good to find out how the human body works though. On the other extreme there are likely folks that think they are cold sleepers and need big sleeping bags, but they are probably actually sweating at night, more than they need to. They might have more safety margin though, but perhaps also more at risk in some ways. Apparently cold acclimatized folks have less blood volume in winter, so they are less prone to heart attack or stroke caused by high blood pressure and a sudden cold shock. Perhaps moderation is best, in all things, including moderation. <img src="/forums/images/graemlins/wink.gif" alt="" />

Here is that iceman runner. I wonder how he sleeps?
http://www.youtube.com/watch?v=madoDvtKEes

p.s. Extrapolating to colder temperatures.
I think once you have figured out what you need for 40F, which might be half of what most people recommend at 40F, you would still need to add the same number of inches as everyone else for every 10 degree drop in temperatures below that, or about 1/2" total loft (top and bottom) for every 10degF. I think it would be dangerous to assume that if you need half the bag at 20F then you might only need half the bag of someone else at -20F. Everyone cranks out about the same kcal/hour per square meter. The only difference is that some people might be using the body as an extra 1/2" of insulation, and others might be sweating a little and negating 1/2" of their sleeping bag, but I think from that point on everyone needs about 1/2" total loft (top and bottom) per 10 degF.

Here is Mark Verber's page on sleeping systems which is really well done. I guess I am saying that acclimatized folks could get acclimatized to using just 2" of total loft at 40F, perhaps even just 1" total loft, but they would still need to add 1/2" total loft per 10deg the same as everyong else, and they should probably put some of that safety factor back into their bag and not plan on waking up cold on an extreme night on a long trip. I think its safe to skimp in summer, below the treeline, if you know its a short night and the temperature can't drop below 40F. You can always get up and dance. Winter is a different story. I think the Army recommendations below 40F are solid.
http://www.verber.com/mark/outdoors/gear/sleep-system.html

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