Mar 20, 2007 at 10:23 pm #1222459
@bugbombLocale: South Texas
Companion forum thread to:Mar 21, 2007 at 5:40 am #1383007
@dondoLocale: Colorado Rockies
Nice work, Will and Janet. I think you outdid yourselves this time. Looking forward to parts 2 and 3.Mar 21, 2007 at 8:57 am #1383028
@kdesignLocale: Mythical State of Jefferson
A very nice article, just the way I like them on this site.
Personally I opt for the liner/vbl sox/merino wool outer sox system in my trailrunners. Sometimes I forego the outer sox entirely. It has worked for me, here in the PNW on day hikes as well as bumming around base camp on extended ski tours as a respite from my ski boots and in conjunction w/ a lighter weight mtneering boot, for fast and light alpine climbing.
I bloody stay away from Gore-tex footwear. They are generally not very breathable nor waterproof (as pinholes or worse develop in the membrane).Mar 21, 2007 at 10:17 am #1383048
@paddsterLocale: western NY
I love the article. May I ask if folks have in fact found vapor barrier socks too uncomfortable at temps above the mid 20's? I know I see this comment quite often, but in practice I have found comfort in using such foot coverings (I use and swear by the RBG vaportherm socks with velcro attached to the top to seal them in) into the 40's. If I do not do that my feet get cold as soon as I stop from the sweat caused by exertionMar 21, 2007 at 10:37 am #1383051
@kdesignLocale: Mythical State of Jefferson
I find them pretty comfortable into the mid-30's or so. VBL clothing or sleeping bag liners would be a different story.Mar 21, 2007 at 11:15 am #1383060
@brianleLocale: Pacific NW
I've never used VB socks (or VB anything). I definitely agree that gore-tex shoes ultimately get wet and take too long to dry, but I'm concerned by the number of layers implied to deal with 25 degree F or lower temps — liner, VB, warmth layer(s), shell. Seems like I not only need a longer but a wider shoe (!).
I'd appreciate if someone were to provide reliable weights for the various VB sock options: Stephenson's Warmlite, RBH, Integral Designs.
If I do the Sierras on the PCT next year, what are the odds I'd have to deal with much in the way of 25 degree or lower temperatures? I like the idea of a VB sock for in camp or at breaks, however, just to keep my newly-donned dry socks dry, plus to act as a backup in case temps get lower. Would be great to get the lightest weight option of these (plastic bags don't weigh much …).
Thanks for a very detailed article (series) addressing something I'm keenly interested in!
Brian LewisMar 21, 2007 at 11:48 am #1383062
I use a liner sock, VBL (bread bag), and wool insulating sock in temperatures from sub-zero to about 30 degrees. I don't think they get uncomfortably moist, but that will vary from person to person. It definitely keeps my feet much, much warmer and I can carry 3 or 4 liner socks and only 2 insulating socks (heavier) because the insulating socks never get wet from perspiration (I still carry the spare because if I break through some ice I need dry socks to change in to).
I use waterproof boots, either the double shell Telemark boots when I'm skiing, or GoreTex lined light hiking boots if I'm hoofing it. I find that in truely cold conditions wet out isn't a problem (If you are melting that much snow on your boots you either need better insulation, or you are working too hard).
Caveat- I am not an adventure racer. I'm of the philosophy that sweating in the backcountry in cold conditions is Dangerous because often I have little or no support. I know that other people feel differently. This is only my two cents.
RegardsMar 22, 2007 at 2:18 am #1383155
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> I'm concerned by the number of layers implied to deal with 25 degree F or lower temps — liner, VB, warmth layer(s), shell. Seems like I not only need a longer but a wider shoe (!).
But I think that IS what Will and Janet say to do: consider going up in shoe size. Hey – a half size increase in a pair of joggers is hardly as bad as plastic double boots with felt inners!Mar 22, 2007 at 6:50 am #1383163
@williwabbitLocale: Southwest Colorado
We only mentioned shoe size without elaborating very much. Many snow travelers have an extra pair of shoes or boots 1 to 1.5 sizes larger than their normal size that are dedicated to snow travel and snow camping. Ryan Jordan's are 1.5 sizes larger so he has plenty of room for the extra layers and not be too tight. Janet and I went 1 size larger. The trick is to wear oversize boots and adjust your socks so the fit is just right, not too tight, not too loose.
Best, WillMar 23, 2007 at 2:41 pm #1383341
"The skin is a highly sensitive organ that likes the air temperature around it to be about 75 °F (72 °F for the hands and feet, and about 78 °F for the head and neck) and a relative humidity of about 70-80%. It releases heat and water vapor (called insensible perspiration) to maintain those conditions in the boundary layer next to our skin. When that protective boundary layer is disrupted the skin reacts to restore it. If you overheat, the sweat glands in your skin start pumping out water vapor to cool the boundary layer back to the comfort zone. If you chill, the sweat glands shut down and your body starts to shiver, again trying to restore the boundary layer to the comfort zone."
With all due respect to Will, I don't think any of the above statement is based on accurate human physiology. Although I am glad to see that one other myth is discussed, sadly, the article continues to propagate several other outdoor community-perpetuated thermoregulation myths.
1. Insensible perspiration is not "given off" by the skin for the purpose of moistening skin. It is a passive process (not under thermoregulatory control) that can lead to moist skin if the skin is covered as in wearing shoes. Sebum probably has more to do with preventing skin from drying out.
2. Thermoregulation is controlled by the hypothalamus with the skin merely an intermediary in the process.
3. Human skin does not release heat to maintain skin surface temperature or humidity.
4. There is no such thing as a boundary layer determining what the sweat glands do. For thermoregulation purposes during exercise, sweat glands are controlled by the brain which reacts to core body temperature and not to skin surface temperature or humidity.
I have been looking into how and why these statements came into the outdoor community books and websites for awhile, including reviewing multiple journal articles extending back to the 1960's and looking at current physiology textbooks, and none of them mention it. From a few emails with Rick Curtis of Princeton University, he gave a 1960's article as establishing it as truth. I read the article he cited and it said nothing of the sort. He said he would look into it himself and edit his website if he found otherwise. I have my doubts whether he really cares about stating accurate physiologic principles on his website or in his book.
How these statements originally found a way into outdoor books is speculation on my part. If one wanted to sell wicking fabrics or maybe even vapor barriers, many would hype some old study and establish it as "truth" for marketing reasons. I would ask the BPL staff to at least go to the physiology or medical community and not outdoor books and ask about those things if no one is interested in listening to this medical doctor. I only bring it up for accuracy sake, no other reason.
There is some very good information in the article also. I don't mean to harp only on what I disagree with : ).Mar 23, 2007 at 7:08 pm #1383363
@jbairdLocale: Deleware Watergap A_T
Will and Janet:
Outstanding, can't wait for the rest.
Thanks for your hard work and dedication.Mar 23, 2007 at 10:05 pm #1383375
@terraLocale: Sydney, Australia.
Thanks for a very thorough article. I hope to employ a lot of this info when (if) I get to snowshoe this year. I'd like to leave the scarpa boots at home and try a lighter, more comfortable alternative this winter.
BTW I thought the "If you're feet are cold, then put on a hat" saying was more due to the body's SENSITIVITY to heat loss around the head/neck not the amount of heat loss. I've never heard the "75% heat loss.." bit of the myth so we might be talking about different folklores ;-)Mar 24, 2007 at 2:47 am #1383378
The blood vessels (specifically the small arteries) in the head do not constrict like those in the arms and legs. In the arms and legs this reduces the amount of core heat lost to the environment. Because the brain gets first dibs on oxygen, the bloodflow to the brain, and the rest of the head doesn't get reduced when it gets cold. So, if you don't wear a hat you turn your head into a heat exchanger, pouring your core heat into the environment. A higher core temperature means that your body will release the constriction of the arterioles in your hands and feet a little, making them feel warmer.
Of course, the surface area of the limbs is greater than that of the head, reducing the impact of this phenomenon. I think a better way of thinking about it is that any heat saved, be it at the head or elsewhere, will make the whole body feel warmer to some degree.
Aint physiology grand?
Andy GilbertMar 24, 2007 at 7:51 am #1383394
"The folks at the Wilderness Medicine Institute ran an experiment on student volunteers and found the rate of heat loss is relatively the same for any exposed part of the body. A person does not lose heat significantly faster through the scalp than any other portion of the body with the same surface area."
I wasn't able to find the study by the Wilderness Medical Institiute, but the study in the Journal of Applied Physiology would suggest otherwise.
J Appl Physiol 10: 235-241, 1957;
Heat Losses From the Human Head
Gerd Froese 1 and Alan C. Burton 1
1 From the Laboratory of Biophysics, University of Western Ontario, London, Canada
A simple gradient calorimeter was developed for measurements of nonevaporative heat loss of the head, and used on three subjects, with heads unprotected but the body adequately clothed, at temperatures between 32°C and – 21°C. Heat loss was linearly related to external temperature by the regression equation (correlation coefficient 0.97 ± 0.01), H = (284.8 – 7.55 x t°C) in K Cal/m2 of head per hour. This means that at –4°C the heat loss from the head may amount to half the total resting heat production of the man. The insulation of the tissues of the head was calculated as about 0.4 clo units, and did not change with the external temperature. To see if it would change if there was general vasoconstriction or vasodilation, a second series of experiments was carried out: a) at 10°C with the subjects unclothed; b) at 20°C with the subjects clothed; and c) at 29°C with subjects clothed and with a heating pad on the chest. While the tissue insulation of the finger increased by a factor of six times in (a) compared with (b), that of the head was constant. In (c) the tissue insulation of the head decreased slightly, indicating slight vasodilation. The importance of insulation of the head in the cold to extend the tolerance time is pointed out by practical examples.
This would support Andrew's statement that head will not vasoconstrict (except for maybe surface vessel in ears, nose etc.) in cold weather, while the limbs do. This held true for clothed and unclothed subjects. Therefore you do lose more heat per unit of surface area from the head than other parts of your body. The bottom line is that if you are appropriately dressed at a temp slightly below freezing (-4 deg C) you lose 50% of your heat through your head if you neglect to cover it. This is linearly related to temperature so if you want to calculate it for other temperatures you can use the equation in the abstract.Mar 25, 2007 at 9:49 am #1383466
@ericlLocale: Northern Colorado
Nice article on a VERY much needed topic. I've also used VBs in temps just a little higher than stated with good results, but those were exceptions.
One trend everywhere is to give info on products as solutions to nearly every problem. While one of the reasons I subscribe to BL is to learn about some of these products, I also appreciate simple do it yourself solutions, and let the reader decide.
I use ordinary foodmarket vegetable bags as VB liners. Very thin nylon sock on foot, VB over it, then nice cushy wool type sock on the outside. In cold footsoaking conditions I've even put a thicker VB outside my thick sock, thereby helping my insulation stay dry both inside and out.Mar 26, 2007 at 8:32 am #1383553
A little more clarification of my remarks above (where I corrected one of my errors), from Medical Aspects of Harsh Environments, Volume 1, Chapter 2, HUMAN ADAPTATION TO HOT ENVIRONMENTS
Integration of Thermal Information
The central nervous system integrates thermal information from core and skin. Receptors in the body core and the skin transmit information about their temperatures through afferent nerves to the brainstem, and especially the hypothalamus, where much of the integration of temperature information occurs. The sensitivity of the thermoregulatory responses to core temperature allows the thermoregulatory system to adjust heat production and heat loss to resist disturbances in core temperature. Their sensitivity to mean skin temperature allows the system to respond appropriately to mild heat or cold exposure with little change in body core temperature, so that environmentally induced changes in body heat content occur almost entirely in the peripheral tissues. For example, when someone enters a hot environment, his or her skin temperature rises and may elicit sweating even if there is no change in core temperature. On the other hand, an increase in heat production due to exercise elicits the appropriate heat-dissipating responses through a rise in core temperature.Mar 26, 2007 at 12:45 pm #1383597
@ewolinLocale: Hampton Roads, Virginia
I understand that people have had great success in seriously cold weather with very light and highly breathable footwear, little more than tall insulated booties with a not very stiff sole. The insulation is thick and goes up quite high, almost to the knees.
Also, in winter I always carry down or synthetic booties, the kind with the thin insulated sole. These are low calf height, very thick and very light. It feels wonderful to take off your X-C boots after a day of skiiing and put on down booties. Guaranteed toasty toes until you leave the next morning.
And if you never have walked in fresh-fallen snow in down booties, you haven't lived!Mar 27, 2007 at 9:41 am #1383710
@pjLocale: LazyBoy in my Den - miss the forest
A truly excellent article – one that i will need reread again to absorb all of the great info contained in it. Kudos to Will and Janet.
one thought that i'd like some feedback on, regarding…
>>"Many experienced snow travelers have dedicated shoes that are one to one and a half sizes larger than their normal shoe size. It’s very important that winter footwear fits loose so it doesn’t restrict circulation. A snug fit may be ok, but you should be able to wiggle your toes within your shoes."
Whether it's a function of the shoe's/boot's "Last" or of the "Sole", or a function of both combined, most footwear is designed to flex at or around the "ball of the foot". I found out years ago when my foot was properly measured by a Red Wings Shoe store manager, that i was wearing the wrong size shoes – typically 1/2 to a full size too small, depending upon the shoe. I was told that the proper way to measure not just my foot, but anyone's foot was from the heel to the ball of the foot, NOT to the end of the toes. See, my toes are particularly short/stubby and my arches are very, very high (so high i was almost disqualified from military service during the draft years in the early 70's). So,…
based upon that measurement, viz. to the ball of my foot, i should take a larger size. The reason was that the ball of my foot should be located on or near the area that the shoe/boot was intended to flex at when "stepping off" while walking. The footwear is intended/designed to flex there and may be stiffer elsewhere along its length – both in front of and behind the intended flex zone.
So, what's all this got to do with the above quote from the article. Here's what i'm thinking and would like f/b on. I think that since ROOM is not just required in front of the toes, but all around (to some degree – yeah, we could lace looser, but, particularly in my case with higher arches – less room for that) that shoes might fit better if only 1/2 size larger (instead of a full to 1-1/2 sizes larger) AND A WIDER WIDTH which would accomplish at least four things to my way of thinking:
1) still give more room in front of the toes and to the sides of the toes
2) give more room on the side of the feet (and heel??? will the heel slip???) since more sock(s) thickness is there too due to layers
3) give sufficient room above the instep/longitudinal arch area for proper lacing
4) KEEP the ball of the foot IN/NEAR the PROPER FLEX AREA of the shoe/boot.
In many/most cases (depending upon one's specific foot) would this +1/2 size, +width solution be preferable to +1size or +1-1/2 sizes with only a small increase in width associated with the larger shoe size? Keep in mind this more drastic size change in length (1-full to 1-1/2 sizes) causes the ball of the foot to be misplaced to a possibly less flexible portion of the shoe/boot. Is this as much of an issue as the Red Wings Shoe store manager communicated that it was?
What do y'all think?Mar 27, 2007 at 8:00 pm #1383802
@dondoLocale: Colorado Rockies
I think you may be on to something here, pj. A few years ago, I tried going up a full size for winter use and the shoes just didn't feel right. The pair I used this winter is sized up just half a size. GTX socks over a thin wool sock fit well inside them. I tried also going wider but I have a narrow heel and found that the shoe slipped too much. So for colder weather I used cyclists' fleece lined neoprene booties over the running shoes.
That said, it seems to me that the research and testing Will and Janet did is very impressive. I'll be reading their series of articles on winter footwear carefully and am sure that I'll be getting lots of new ideas from them.Apr 2, 2007 at 2:01 am #1384513
Excellent article; I will read it a few more times to absorb all of its knowledge. However, I must disagree with your debunking of the head heat loss 'myth'.
You mentioned the WMI study which found the rate of heat loss is relatively the same for any EXPOSED part of the body. A person does not lose heat significantly faster through the scalp than any other portion of the body with the same surface area.
Agreed, of course, but we are not talking about covering a head when the body is "exposed". The concept of putting a hat on to dramatically reduce heat loss is applied when a person is heavily insulated with clothing to a few clo everywhere except head and maybe hands. In this case, there is very little heat loss from the well insulated portions of the body, and most of the heat loss is lost throught the un-insulated head through conduction, convection, and radiation. Putting an insulated hat on in this case would dramatically reduce the overall body heat loss. A balcalava would be even better.. For example, if the head is 10% of the body and .4 clo, and the remaining 90% was at 3 clo, a rough calculation shows 75% of heat loss would be eminating from the head (7.5x as fast from the head, but it's only 10% of the body; thus 10% of 750% is 75%).(Richard can you do a more proper estimation?)
In my personal experience skiing and hiking in cold dry conditions, the easiest way to 'dial' in a temperature is to indeed, add or remove a hat. Its no myth; when the body is heavily insulated, the head is the primary source of heat loss.Apr 2, 2007 at 10:55 am #1384572
Brett, the myth is making feet warm by wearing a hat. There would be no frostbite of the feet if wearing a hat prevented it. That saying is an oversimplification to get people to understand the importance of wearing a hat in the right conditions, but it has no significant physiologic accuracy.
You could go climb Everest with a -20 F sleeping bag on your head, but if you don't properly insulate your feets too, you gonna lose them toes.
The Easter BunnyApr 2, 2007 at 7:48 pm #1384626
Thank you Easter Bunnny.. I will avoid wearing a sleeping bag on my head while walking barefoot in the snow.. from now on I mean.. ;)Apr 4, 2007 at 11:38 am #1384805
@brianleLocale: Pacific NW
I'm hoping to through-hike the PCT next year, so am trying to figure out my gear this year — this article series is a great basis for thinking through the Sierras stretch.
I was able to do a morning hike yesterday starting out at 22 degree F in snow, wearing a mesh watershoe (Columbia Aquatooth) and Rocky Gore-tex socks over a wicking sock and a wool sock. It took a bit to get over my visceral reaction of "this is crazy" (this article gave me the confidence to try it), but it worked just great. My feet got mildly cold at times, but never painfully so, and after 3 hours of hiking fairly steeply up and then back down I was amazed at how dry my liner and wool socks were.
What particularly sells me on this system is the idea that I don't have to care if my shoes get wet — they'll get wet, but they'll dry much faster than supposedly waterproof shoes or boots that I wouldn't want to be committed to on a many-day trip in snow.
The one caveat I have is in getting the sizing right. In "normal life" I wear a size 10 shoe. I got size 11's in the mesh shoes, for obvious reasons. So I ordered a size 11 gore-tex sock. Barely fits me. Yesterday afternoon I found I was developing blisters on the outsides of my second-to-smallest toes (both of them); I suspect this is due to the size of the Gore-tex sock, so I'll probably buy a pair of size 12's (!). If that doesn't work, then a bigger shoe. Getting the sizing right is likely to take some iterations, and expense. And once I get it right for "now", I'll have to factor in the odds that my feet will be larger by the time I hit the Sierras …
Thanks, BPL, for such a detailed (and for me, timely) article series.
Brian LewisApr 8, 2007 at 9:14 pm #1385269
"Replacing that heat with a hot beverage is a good way to maintain core temperature and stay hydrated, while drinking ice cold water puts more demand on your body’s metabolism to produce heat."
My experience agrees with this–if I drink a liter of hot tea (by the way, that's quite a bit for one sitting), as I do just about every morning, I feel very warm. But that doesn't make much sense! A liter of water at 50C (I don't know the actual number, but that's close to scalding) contains 50 more Calories than a liter of ice water. That's utterly dwarfed by the Calories taken in by an energy bar.
Is it that while the energy bar's energy takes a while to make it into the system, that liter is applied over 20 minutes? 50C/12min (gulp!) is 4C/min; the article says you should be eating 300-400C/hour, which is 5C/min. So the liter of hot drink maybe doubles your caloric intake for a few minutes–is that what's going on? Is it enough to explain the heating?
If I eat two power bars, will my skin feel warm? No. Is this just a situation in which one kind of energy can be regulated but the other can't?
Or am I missing something else?
The case of hot food is far more extreme. Here, you can expect to take in 800C in a meal, maybe 20C of which is thermal. But I do love a hot meal :)Dec 8, 2007 at 2:01 pm #1411806
Riveting article. A most read.
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