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The Science of Warmth

 
The Science of Warmth

Page Type: Article

Object Title: The Science of Warmth

Activities: Hiking, Mountaineering, Trad Climbing, Sport Climbing, Toprope, Bouldering, Ice Climbing, Aid Climbing, Big Wall

 

Page By: Duseks

Created/Edited: Nov 24, 2007 / Dec 5, 2007

Object ID: 359562

Hits: 36912 

Page Score: 97.16%  - 68 Votes 

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Introduction

There's a multitude of theories and personal preferences when it comes to staying warm. Possibly the only uniting factor amongst these hypotheses is that they share the same goal - fighting off the cold. This article will explain the basic principles of what creates and maintains warmth.

Facts

Average human body core temperature:
98.6°F or 37°C. On an individual basis this varies a few degrees Fahrenheit and about one degree Celsius.

Average human skin temperature:
about 92°F or 34°C. This varies greatly based on many factors.

Hypothermia:
a potentially fatal condition that occurs when body temperature falls below 95°F or 35°C

Heat Generation

Internal Sources:

Human produced heat is generated through "burning" calories. Essentially when your body uses energy heat is created. Higher levels of physical activity produce more heat.

Between the temperatures of 65°F and 130°F the body relatively easily maintains its normal core temperature at stasis (non-activity).

Core Warmth
When your core (torso) is warm it readily releases blood to the extremities. When your core gets cold your body's natural defense is stop sending blood to the extremities and keep it for vital organs and the brain. Therefore the best solution for cold hands and feet is often to heat up your core. Core warmth is most easily achieved through physical activity but increasing insulation is another option.

External Sources:

There are too many external heat sources to list but anything warmer than the ambient outside temperature or normal body temperature is a possible external heat source. Some common examples:
  • Hot food or beverages
  • The sun
  • Fire
  • heat packs

What It Means to Us:

Heat generation is based on activity level. Our clothing system should match our activity level in order to maintain desired body temperature. The fuel sources available to your body via diet also affect its ability to generate heat. The most important part of your body to keep warm is your core.

Heat Loss

Your body creates heat, but we can still get cold, how is that possible? Through heat loss. Heat is lost in four ways:

Conduction:
When one object touches another object the warmer object transfers heat to to the cooler, thereby losing heat.

Convection:
The transfer of heat by circulation or movement of heated parts of liquid or gas. Basically your body loses heat to the air via conduction > that air blows away > new air replaces it > grabs some heat > blows away - and so forth.

Radiation:
To make a long story short your body releases electromagnetic waves and in doing so loses heat. This happens mostly in your head, but also through your hands and neck.

Evaporative Cooling:
Your body transfers heat to perspiration > perspiration evaporates and in doing so takes heat with it, this is evaporative cooling and it is the human body's method cooling itself.


It should now make sense that if you lay on cold ground your body conducts heat to the ground and you get cooler. Meanwhile the cold breeze steals heat through convection. Your hatless head radiates heat away, and your wet clothes lose heat as they dry.

Insulation

Insulation is material surrounding a body to slow heat loss. The idea is to create a layer of trapped air called a "dead air space". Your body heats this air and it surrounds you like a warm blanket.

The dead air space still loses heat to the surrounding cold, yet still keeps you warm. This is possible because the cooling process is slowed by trapping air and moving the interface of warm-meeting-cool air away from the body. The air closest to the outside loses heat to outside elements, but your body is constantly heating the air behind it and giving it new heat, so you remain surrounded by warm air (insulation).

The degree of insulation depends on two factors: Loft and Fabric Breathability

Fabric Breathable

Fabric breathability refers to the degree to which a material allows moisture and air to pass through it.

Sealed fabrics are warmer than breathable fabrics - but countervailing factors often offset any benefit sealed fabrics offer. Non-permeable fabrics such as vinyl and rubber do not allow any air or moisture to pass through them. This traps air more effectively between your body and the fabric.

Sealed and low breathability fabrics have a serious caveat. Your body constantly generates moisture, especially when you work hard. Low breathability fabrics do not allow this moisture to effectively escape. This leads to moisture buildup between your body and the fabric, which is not only uncomfortable, it is potentially dangerous - being wet when it's cold is bad.

Breathable fabrics allow moisture to pass through them, the moisture generally evaporates on the outside of the fabric and becomes a non-issue. The moisture does cause cooling as it evaporates (evaporative cooling) but the interface is moved away from the body, which gives the body time to heat a protective layer of air behind it.




Loft

Loft refers to the distance between your body and the outside elements created with insulating materials (clothing). The distance creates a "dead air space". All other considerations held equal - the higher the loft the greater the insulating power > the warmer you stay.

Loft is only effective if the air space it creates is "trapped". If air passes straight through the loft with little or no resistance, it escapes too quickly to insulate effectively. If wind passes through the loft easily, warm air is washed away. On the other hand if the outer fabric is too sealed water buildup becomes an issue.

In order to trap the air that loft creates outer layers should be wind resistant or proof. Breathability should remain a concern because moisture must be allowed to escape. There are many modern materials that fall along a continuum of trying to achieve wind resistance vs breathability.

If an outer layer that traps air, such as a hardshell, windshell, or softshell, is worn - then under layers do not need to be weather resistant. Materials such as waterproof, windproof, or resistant membranes and/or facing are common on fleece and pile jackets. These materials improve the performance of garment when it is used as the outermost layer. These materials do not add appreciable loft (the fleece, pile, or other faced fabric does that), so when they are used beneath an air trapping layer they add extra weight and inhibit moisture transfer without adding significant warmth. Once an outer air trapper is established, in the interest of warmth, the only important thing to create underneath it is loft. Standard no frills no "weather resistant" materials added fleece or pile breathes dramatically better, is lighter, costs less and dries faster - making a more suitable under layer.

Many climbers still use weather resistant mid layers, and there are good reasons to do so, but it should be noted that you can save a lot of weight and money by using basic breathable layers and throwing a super light wind shell over the top to provide weather resistance.

Diet

What you eat and your level of hydration strongly affect your warmth.

Food

Your body creates heat by burning calories. If you don't have adequate calories available to burn it's harder to stay warm.

Fat contains more calories per gram than carbohydrates or protein - so given the same weight of food - a diet higher in fat will be warmer than one low in fat (assuming the fat will actually be burned).

Spicy foods naturally raise the metabolism and hence speed up the heat making process. Ginger has long been known to help keep you warm.

If the amount of Calories is held equal, food that is warm won't take heat away from you, and hence keep you warmer.

Hydration

Adequate hydration is critical to staying warm. Water is amazing at retaining heat, so keeping your body properly hydrated means that there's more material in your body to retain warmth with.

-much more to be added-

Staying Cool

Climbers generally prefer to not stay sweaty, so they pick fabrics that "breathe" and wick well, which is to say they don't absorb much water and air passes through them relatively easily.

Cotton may kill, but it actually keeps you cooler than wicking fabrics by retaining more water and prolonging evaporative cooling. Your body actually needs to perspire more in wicking fabrics to maintain an effective evaporative cooling rate.

Wicking fabrics are still preferred by most climbers, myself included, because of increased comfort (no wet feeling), you are more dry when activity stops, and there's less risk of becoming to cold if the temperature suddenly drops.

Water evaporates fastest off of bare skin. Sun burns are another possible issue with uncovered skin. It may seem counter intuitive to wear long sleeves and pants when it's very hot, but it can actually keep you much cooler. Check out the people that live in the desert, whay are they in cotton from head to toe?

Utilizing External Heat

Black and darker colors absorb more heat that white and lighter colors. Hence most belay layers are dark in color. Wearing darker colors will keep you warmer in the daylight hours. Darker colors of the same fabric also dry faster.

Shared tents are warmer than solo shelters or bivies. Smaller shared tents are warmer than large ones. Snuggling up to your partner has obvious benefits... and obvious issues :) In extreme situations sharing a sleeping bag or bivy sac can save both of your lives. Many a partners toes have been saved through contact with a warm partners skin.

Heat packs are lightweight and usually work well. Some don't work at altitude.

Lukewarm and warm liquids don't require you body to heat them - they'll keep you warmer.

Boiling water is a climbers best friend. Keeping it next to your body will not only give you it's heat, it will slow it's cooling - meaning you won't be drinking cold water later.

Fumaroles stink - but they're warm. Hot springs are awesome.

Fire is a great heat source, just make sure it's safe, non-damaging, and respectful.

Angry people are warmer than happy ones - so if you're partner's being an asshole maybe he's just trying to keep you warm :)

Natural wind blocks greatly reduce convective heat loss.

General Clothing System and Names

Clothing Systems for climbing are generally built around trapping heat or letting it escape. Let's assume we're in a cold environment.

        Layer 1:         Next to skin        (base layer)

When you're working hard you tend to sweat. Even if you're cool while working your body still creates localized perspiration and general moisture. For this reason most climber choose a moisture "wicking" fabric for their first layer. These fabrics move moisture away from the skin quickly and allow moisture to evaporate rapidly - this minimize the evaporative cooling.

        Layer 2:         The intermediates         (layers)

Intermediate layers create loft and may or may not trap air for use as an outer layer. Common Fabrics: non-lined fleece, lined fleece, softshells, pile, and wool.

        Layer 3:         Wind and Rain         (shells)

This layer block the wind, and the rain (or other external moisture) if desired. Many climbers opt out of this layer by combining a mid layer with this layer (this is called a "softshell"). The desired effect is to block the elements and trap heated air.

        Layer 4:         The Belay layer         ("down jackets" "belay jacket")

Most climbers don't wear large down or synthetic jackets or pants under other layers, although thinner versions are commonly used as mid layers. Instead, when it's really cold, most climbers add a down or synthetic jacket and/or pants over their existing layers.

Common Fabrics

Base Layers:
          • Polyester - wicking, low water absorption, soft feel
          • Nylon - wicking, low water absorption
          • Lycra and Spandex - added to the above to create stretch

Mid Layers:
          • Fleece (non-lined) - lightweight, almost no water absorption, high loft, wicks rain
          • Fleece (lined) - same as above but with a bonded nylon layer that blocks wind and rain
          • Fleece (stretch) - fleece bonded to a nylon/spandex layer. Higher water absorption, better movement
          • Pile - mid weight, low water absorption, sheds light rain, good wind resistance
          • Wool - mid weight, low water absorption, sheds light rain
          • Schoeller soft shell fabrics
          • Polartec Powershield soft shell fabric

Shells:
          • Gore-tex - standard waterproof breathable membrane
          • Gore XCR - same waterproofness as standard g-tex, lighter and more breathable
          • eVent - same waterproofness as standard g-tex, lighter and more breathable
          • SilNylon - silicon impregnated nylon, blocks wind and rain, low breathability
          • DWR - durable water resistant coated fabrics, shed light rain, usually windproof
          • Company Specific - most companies have their own g-tex knock off it usually functions about the same.

Belay:
          • Goose Down - the "warmest" material known to man, almost useless when wet.
    Synthetic Insulations:
          • Polarguard
          • Primaloft

Common Theories: Action Suit vs The Layering System

The Layering System camp uses more intermediate layers to achieve the desired temperature. The belay layer is often omitted in favor or more "static" layers. Layers are added and removed to maintain temperature.

The Action Suit camp (coined and championed by Mark Twight) believes in wearing only a few layers that are rarely or never taken off during high activity levels. During colder periods and/or low activity a belay layer is donned.

The main difference is what is frequently removed and added - intermediate layers vs a belay layer.

Tips

-Utilize natural shelters
-If you carry the layers, why not sleep in them too?
-Boiling nalgene in the sleeping bag... aahhhhh... so nice... check the seal!
-Eat fat before bed
-Start cold, work cold, chill warm (the puns I tell ya!), camp warm
-You can put boiling water into platypuses, other bladders warp the seal
-Don't wait to add more layers when stopping for prolonged periods
-Use heat packs
-Understand your layers, why will they keep you warm?

Conclusion

Warmth is generated internally and externally.

Creating trapped dead air space insulates the body. The amount of trapped dead air space is determined by loft. The "trap" is determined by the breathability of the outer layer of fabric over the loft.

Most of the marketing directed at consumer is bogus - the concepts that keep you warm are simple and basic.

Balancing what happens to your sweat makes a big difference in your temperature control.

Your diet affects your warmth.

Hydration affects your warmth.

Physical activity is the most influential factor in your warmth.


-This article mostly done, but I'm tweaking it, if you feel compelled to vote negatively please PM me first so I can address you concerns. I love feedback.

Image Citations

The images used in this article are provided courtesy of these sites, listed in order:

http://www.holidaycityflash.com/article%20pix/frostbite.jpg
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/images/irbody.jpg
http://www.rspb.org.uk/Images/canada%20goose_300_tcm9-139738.jpg
http://www.rtctextiles.co.uk/images/photos/barrier.gif
http://www.needlesports.com/acatalog/rabexpedition_downsuit.gif
http://www.earthfoot.org/places/ly001z.jpg
http://cires.colorado.edu/images/people/t/twightM-a140.jpg

Images

User Profile Image

Comments


[ Post a Comment ]
Viewing: 1-20 of 26 « PREV 1 2 NEXT » 

nikolai7910 points

nikolai79

Voted 10/10

Although the article is under construction... I find the article very interesting.
Posted Nov 26, 2007 6:33 pm

BartRe: 10 points

Bart

Voted 10/10

same here, nice work.
Posted Nov 27, 2007 3:25 am

nikolai79Just a suggestion...

nikolai79

Voted 10/10

Please add some picture to illustrate the article as soon as you can.

Thanks again for this article.

Regards from Spain ;-)
Posted Nov 27, 2007 5:02 am

nikolai79Re: Just a suggestion...

nikolai79

Voted 10/10

Good images dude!
Posted Nov 28, 2007 12:32 pm

Diego SahagúnVasoconstrictors

Diego Sahagún

Voted 9/10

You could talk about them and their relation with cold. For example, caffein.

Gracias

Posted Nov 27, 2007 9:44 pm

vanman798Great Idea!

vanman798

Voted 10/10

I think this is a great idea for an article. I enjoyed reading it. I noticed one spelling mistake under "Staying Cool" you typed "whay" instead of "why".

I suggest you add captions to each of the pictures in your article.

Thanks for writing this article.


By the way, a trick used on fishing boats "back in the day" to help keep toes warm was to rub red cayenne pepper (capsicum) on them, or sprinkle the pepper in one's socks. Capsicum stimulates circulation.

Also, keeping the lower leg warm, via gaitors (for example), helps keep the toes warm. By the same principle, placing a chemical hand warmer in the sock at the ankle, will help the toes to stay warm. The principle here is that the blood circulating through the foot is warmer coming in if the lower leg is warm.
Posted Nov 28, 2007 3:19 pm

dpkdetails

dpk

Hasn't voted

any details on how long the exposure that resulted in the heavy frostbit fingers?
Posted Nov 29, 2007 8:58 am

Dmitry PrussLots of terrain not covered

Dmitry Pruss

Hasn't voted

early detection, prevention, tratment of frostbites

treating hypothermia

circulation issues (activities and wear enhancing and reducing circulation)

legends about alcohol, smoking, and drugs

science of chemical warmers

...
Posted Nov 29, 2007 2:56 pm

DuseksRe: Lots of terrain not covered

Duseks

Hasn't voted

I agree, there's a lot more that could be covered. I always try to make my articles clear and concise, so that the general browser is able to get a lot of information without glazing over on tons of details and exhaustive scenarios. On other all that extra information is really useful, especially to people who already know a lot about the subject.

I think Vasoconstrictors, consequences of cold (hypothermia, frostbite, etc), circulation issues, altitude (which I may add here), and other topics should be discussed - but I'm reluctant to put them here in the belief that they probably deserve their own article (which could be linked and integrated into this one).

What do you think, add a lot more content to this article or leave it for new articles, maybe a part 2?

-Scotty
Posted Nov 29, 2007 5:03 pm

foweymanstaying cool

foweyman

Hasn't voted

Nice article. I think your paragraph on staying cool could elaborate on the best clothing to wear if overheating is the concern. There is a trade off between evaporative and convective cooling (as you said, bare skin is best) and prevention of radiative heating (and sunburn) by the sun (full skin covering is best). The best solution I devised when running/hiking in the heat and sun was to tie together the sleeves of a long-sleeve cotton t- shirt and put the loop over your head. The body of the shirt is kept wet with cold water if possible and rotated towards the sun so that it shades half your body while the side away from the sun is bare for good heat loss. As you change direction, rotate the shirt to the front, back or sides as needed. It won't score any fashion points but it's quite functional.

Also the reason people are tightly covered from head to toe in the desert is to protect against wind driven sand. If sand isn't a concern, something providing shade and good ventilation is best.

I also appreciate the rarely made point that (despite what the marketers of expensive wicking fabrics say) inexpensive, non-wicking cotton is cooler in the heat than wicking synthetics .
Posted Nov 29, 2007 6:20 pm

camerona91belay layer

camerona91

Voted 10/10

"***If an outer layer that traps air, such as a hardshell, windshell, or softshell, is used - materials intended to trap air on under layers adds and weight and resistance to moisture transfer without adding much benefit. Once an outer air trapper is established, in the interest of warmth the only important thing to create underneath it is loft. "

Does this mean that you should remove your shell before adding a puffy overtop as a belay layer?
Posted Nov 29, 2007 8:35 pm

David Senesacgood start

David Senesac

Hasn't voted

As others have said there is quite a bit more to add. A good start nevertheless to this body of information. Of particular interest would be information about survival strategies in difficult conditions. There is more to keeping warm that our ancestors understood that we modern people likely have yet to discover.

Just the other night I saw one of the PBS Nature series features where one segment had one of we Westerners visiting the Siberian Chukchi people, who live much like our Eskamos but in some of the world's coldests conditions. Their large communal tents are made of reindeer skins and insulated in reindeer fur, and instead of sleeping with say reindeer fur blankets, at least some of the time they sleep within the tent within smaller body sized reindeer fur enclosures. The visitor remarked he was toasty all night while it was tens of degrees below zero outside.

David Senesac
http://www.davidsenesac.com
Posted Nov 30, 2007 4:02 pm

BlairWell Done

Blair

Voted 10/10

Good article, thanks for sharing~
Posted Dec 2, 2007 11:46 am

strat1080Good Info

Hasn't voted

"***If an outer layer that traps air, such as a hardshell, windshell, or softshell, is used - materials intended to trap air on under layers adds and weight and resistance to moisture transfer without adding much benefit. Once an outer air trapper is established, in the interest of warmth the only important thing to create underneath it is loft."

The above statement is kind of confusing and contradictory. You are saying that additional layers underneath a shell do little good and only hinder moisture transport but at the same time saying that loft inside the layer is more important. I would think that adding layers under the shell would add warmth as the warmth retained through the insulating layers will not be lost convectively. In other words, a fleece jacket will do much more good underneath a shell than outside of a shell because it won't generate any heat outiside of the shell in windy conditions. Is this what you are trying to say?

I'm a huge proponent of the action suit theory but this system only works if the insulating layers that go over the top of the suit are windproof or highly wind-resistant.

I really liked the image of where heat is generated in the human body. It really shows the importance of keeping the core warm.
Posted Dec 4, 2007 11:31 pm

DuseksRe: Good Info

Duseks

Hasn't voted

Layers underneath a shell will absolutely add warmth. The point is that if you are wearing an outer air trapping layer and underneath you have a choice between a nylon lined (wind resistant) fleece jacket, a softshell, and a non-lined bare bones fleece jacket - they are all the same thickness - they are all going to add about the same warmth. The softshell and lined fleece jacket are not going to pass moisture as well as the standard fleece, furthermore both other options will be heavier than the standard fleece. So the point is, on mid layers that you intend to wear a shell or some other air trapper over - don't bother with wind or water resistance - just use the lightest/loftiest/best-breathing layers you can get your hands on. This is usually standard non-lined fleece, which also happens to quite cheap.

there's some typos in that statement and I'm still trying to find a way to use minimum words but convey the idea. I'm going to edit it.

-Scotty
Posted Dec 5, 2007 2:29 pm

txmountaineerThanks for such a great article

txmountaineer

Voted 10/10

I've traditionally used Merino wool as a NTS layer, which, based on your article, I now realized has caused me to get colder after activity since it leaves the moisture on my skin.

Thank you so much for this!
Daniel
Posted Dec 5, 2007 1:06 pm

Brad MarshallNice Article

Brad Marshall

Voted 10/10

Nice article Scotty. Just finished reading it while enjoying a cup of java in my SP mug! When are we going to get those little flags?

Brad
Posted Dec 8, 2007 6:23 pm

kunz82414What about my fingers?

kunz82414

Voted 7/10

I typically don't have a problem keeping my core warm; my fingers and toes experience the most discomfort in the extreme cold. Also, can't down be worn as a loft layer? I prefer to have a weatherproof shell outside my down layer when it is possible.
Posted Dec 13, 2007 11:30 am

scottsolinkoGloves

Hasn't voted

Most people first have an issue with their hands getting cold. A lot of the time this isn't because their core is cold, but because they are over dressed and their gloves are too heavy. Their hands start to sweet and soaks the glove, only to freeze when they stop. If the inside of your gloves get wet, they are USELESS. Best also to wear a liner glove and have a few that you can change out when they get damp.
Posted Dec 14, 2007 5:53 pm

Sunny BunsGloves

Hasn't voted

I agree: keeping the fingers warm is not easy. I'm going to try this and see how it works: I'll put on a pair of thin latex rubber gloves first and then put on my insulation gloves. I'll bet my hands stay warm, although they'll be sweaty, but I can live with sweaty hands for a day trip. I'll let ya know how it works.
Posted Dec 14, 2007 8:26 pm

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