There are five different ways in which the body loses heat; radiation, convection, conduction, evaporation, and respiration. The ability of clothing to effectively reduce or minimize heat loss is of primary concern is the design and construction of cold weather outdoor apparel. Let’s examine each of these heat loss mechanisms, three of which apply to cold weather and how proper cold-weather clothing use can minimize that heat loss while providing protection and comfort.
Heat Loss from Radiation & How to Protect Against It
Radiation is when the heat is lost from the body as it radiates outward through the skin, similar to a radiator heating device that radiates heat from its coils outward to warm a room. This form of heat loss is wonderful when you are overheating and need to dispel heat to maintain a normal core body temperature.
The proper use of cold-weather outdoor clothing takes advantage of this heat loss mechanism to trap this heat next to our body, thus using our own body generated heat to keep us warm after it has radiated out from our body. This is the primary function of the “Warmth or Second Layer” of clothing that serves as insulation.
- Fabrics such as polyester synthetic polar fleece, good down, wool, or Gore-tex are excellent insulator materials but also are effective in absorbing sweat while allowing for breathability to help keep you not only warm but comfortable as well.
It is also important to note that the actual “Base or Inner Layer” of clothing aids in this trapping of heat and also serves to wick away moisture that accompanies heat loss through the skin, helping to keep the body and clothing dry.
- Fabrics such as synthetics like nylon, or natural fibers like merino wool or silk are effective in wicking moisture from your body as well as providing a layer of thin insulation.
Heat Loss from Convection & How to Protect Against It
Convection is when air, or wind, moves across your body surface displacing a layer of warm air next to the skin, warm air that has radiated out from your body, thus cooling the body. The greatest convection would occur where the body’s skin is exposed to the movement of air across its surface, creating a draft. There are certain areas of the body that tend to be more susceptible to drafts and therefore special precautions should be taken to eliminate exposure. They are:
- The neck or collar area. The jugular veins and carotid arteries as they run through the neck are fairly close to the body surface and therefore this area is more susceptible to the loss of heat.
- Having a collar that is designed to stand up, can be held in place, and pulled to surround the neck can provide protection against wind and heat loss due to convection. A jacket with a lined hood can also be very effective in protecting against air drafts in this area. For extra protection, the addition of a scarf around the neck is an option. Fabric such as soft fleece can protect this area as well as be very comfortable next to your skin.
- The midriff or waist area. Internal organs such as the kidneys and intestines are located in this area and are sensitive to cold, especially the kidneys. If body core temperature were to drop due to prolonged exposure, in addition to the heat loss from convection, the body would reflexively shunt blood flow from the extremities in an attempt to maintain core body temperature.
- Coats or jackets that are longer in length and fall below the waist or have an extended back length can provide the needed protection here, and those that come with an adjustable inner waist seal allow you to cinch them up effectively eliminating any wind draft in this area.
- The wrist area. The transition between the sleeve of a jacket and the gloves to protect the hands can be an area of high risk for wind drafts. Exposed and cold wrists will lead to cold fingers and an increased risk of frostbite.
- Clothing items, base layers, and jackets, that come with long sleeves or liners that extend further to allow for a hook of material over the thumb help ensure that the sleeves never roll up and expose the skin of the wrist. Jacket and coats that have elastic or stretchy cuffs or Velcro straps help ensure a snug fit around the wrist to prevent exposure to wind drafts.
- The chest and abdominal or zipper area. The zipper literally protects the largest open area of the body – the chest and abdominal area – which contain vital organs. As the teeth of the zipper connect when the zipper is pulled to close the jacket a barrier is created, but this barrier is not a perfect seal, especially against convection forces.
- Coats and jackets that come with flaps that cover the zipper over top and underneath, especially that snap down to lock it in place, can significantly reduce the any draft that might enter through the interlocking teeth.
- Another helpful tip is to ensure that all layers of clothing don’t have zippers that align similarly, but rather stagger them or wear a pullover sweater underneath so that there is no zipper over a zipper alignment.
Heat Loss from Conduction & How to Protect Against It
Conduction is when the heat is lost through contact with cooler surfaces, such as a bench, a pole, a floor, or any object with which a body part may make direct contact.
- All layers of clothing, gloves, and boots help protect against heat loss due to conduction as they all provide a barrier between your skin and a cooler surface. The “Shell or Outer Layer” of clothing, should be waterproof and wind-resistant, and these characteristics ensure a good barrier from contact with cooler surfaces.
Heat Loss from Evaporation and Respiration
These other two mechanisms of how the body loses heat are more important in helping to resist heat-related conditions caused by prolonged exposure to hot and humid environments and are not applicable to this discussion on how to prevent heat loss in cold weather.
What is Next
The continuing innovating in the development of clothing to protect us from the elements has been staggering, with new and improved fabrics and combinations of fabrics that work with the body’s own thermoregulatory process to help maintain as close as possible the body’s temperature in normal and safe levels.
You may also be interested in our other article titled, “What are the Basics of Layering for Cold Weather Outdoor Activity?”