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How to Reduce Heat Loss

     It is necessary to understand that clothing do not provide warmth; they help regulate the heat that the body produces.
     Body heat is lost in many ways; evaporation, respiration, conduction, convection, and radiation. By understanding the above mechanisms, one can better regulate or utilize their insulating equipment.

     Evaporative Heat Loss occurs when the body perspires. When the body is warm, it sends blood to the surface to cool. As the blood rushes to the surface, the pores of the skin open emitting water. Water evaporating in the surrounding air cools the skin. Mountaineers for years have understood that this form of heat loss is one of the leading causes of deaths in the backcountry. You may have heard of the importance of wearing many layers of clothing in order to enhance you ability to regulate body heat. The reason for this is that the human body loses its heat to moisture 25 times faster than to dry air. So, it is very important not to allow the body to perspire too much in the backcountry. If this happens, it is also important not to let the perspiration sit in contact with your skin. Hence the importance of wearing hydrophobic clothing in the outdoors, such as Polypropylene Thermax, Polartec, Capilene, etc.

     Respiration Heat Loss occurs when cool outside air enters the lungs, is warmed, and then is exhaled. In the wintertime many people, without any prior knowledge of this form of heat loss, wear a scarf in order to stay warm. Wearing a scarf controls heat loss through respiration. To minimize this form of heat loss, avoid over taxing yourself and breathing hard.
     Heat always travels from a warm surface to a cooler one. Conductive Heat Loss happens when the body contacts a cooler surface, allowing heat to be lost to the cooler surface. To limit conductive heat loss, avoid contact with cooler surfaces by putting an insulating pad between you and the ground. To bring home this point, it is safe to say that on a cold night an insulating pad is almost as important as the sleeping bag you sleep in. Without an insulating pad, all the heat trapped by your sleeping bag will be lost to the ground.

     Radiative Heat Loss is the escape of infrared radiation from the body. This form of heat loss is minimized by simply wearing insulating fabrics. Also, you may have seen that most long-distance runners are wrapped in a shiny aluminum foil after finishing their race. Aluminized fabrics do a very good job of reflecting the escaping radiation back to the body.

     Convection Heat Loss occurs when body heat warms the air around the body. The warm air then rises away from the body. One can prevent this form of heat loss by trapping this warm air around the body and stopping its escape. Unfortunately, unlike for some animals, this is easier said than done.
In warm-blooded animals, cold air causes blood vessels near the skin to constrict, keeping the warm blood away from the chilled exterior in order to help retain the heat of the body's central core. In animals covered with hair, the constricting of the blood vessels triggers a muscular reaction, causing their hair to stand up, trapping air within it. The natural heat emitting from the body will then warm this trapped air translating it into an insulation layer of warm air around the animal.
     The human body no longer has this thick layer of hair. As the blood vessels near the surface constrict, we get goose bumps. If the surface is not warmed then we shiver, which is a natural muscular reflex to get warm. To really warm up, we must put on an artificial layer of hair, which is clothing.