Staying warm in the great outdoors is an important bushcraft and survival skill. In cold conditions in the great outdoors you can lose heat through numerous different processes – radiation, convection, conduction, evaporation and respiration (breathing).
Radiation: When you rest by a good camp fire and feel its warmth, you are gaining heat radiated by the fire. Another way to look at this is that while you are getting warmer, the fire is losing heat to its environment. It’s the same for you when the surrounding environment is cold: You'll radiate warmth and so lose heat to your environment.
Many people think that heat loss from radiation occurs only from exposed skin. But even if you are dressed, heat radiates from your body to your clothes, then from your clothing to your surrounding environment.
Convection: Convective heat loss happens between a material surface and a moving fluid or gas that is in contact with it. The air nearest your skin is warmed by the body. If this warm air is allowed to move away from your body, less warm air will take its place and more body warmth will be given up in warming this cold air. Putting on insulating layers of clothing helps to constrain warm air near to your body. It’s the air trapped in your clothing that helps you to maintain body warmth, not the clothes themselves.
A good amount of care and attention should be paid to insulating your core body area; the head, neck, trunk and groin. There is certain to be a good blood supply to your neck and head and there is always a lot of warm blood passing near to the surface of your neck. Therefore , it is always good to have a warm hat with you, even in summer. It doesn’t have to be bulky: A merino wool beanie is a great choice. In chillier conditions, you need to also include a head-over or scarf to prevent heat loss from your neck. Those things, though only small, can make a significant difference to how warm you are on a cold day, if the weather turns bad, or if you’ve got to spend an unplanned night outdoors.
Strong winds and low temperatures can conspire to creat the right conditions for great convective heat loss. Unless your shell layer is windproof, cold air passing over your body will remove the warm air and take heat away from you.
Conduction: Heat loss via conduction comes thru contact with cold surfaces or objects.
Aluminum is a very good conductor. Water is a good conductor of heat. Air is a poor conductor of heat. That’s why it is so great to have air captive in your garments to insulate you. It’s good to insulate your body from cold surfaces with a poor conductor. A common example of this is the use of a sleeping mat when camping out. If you sleep directly on the ground, you lose a lot of heat into the earth. If you are building a shelter, make sure you build a good bed, with satisfactory insulation.
Avoid handling cold objects, in particular metal, with your uncovered hands. Don’t touch metal objects with your hands in temperatures much below 0 degrees Celsius (32 degrees Fahrenheit) as they can cause near-instant freezing of skin. Even when you are wearing gloves, limit how much you handle metal objects in sub-zero (Celsius) temperatures.
Evaporation: To convert a liquid to a vapor or a gas requires energy. What this suggests is when sweat on your skin or moisture in your clothing evaporates, this evaporation draws heat away from your body. This is called evaporative heat loss.
Evaporation is a very effective mechanism for dispersing heat. It explains why sweating works so well at keeping you cool. The darker side of evaporation is that if you get wet in a cold environment, you can get awfully cold, very quickly. Hence, it’s vital that you do all that you can to stay dry while in the great outdoors.
Your first line of defence agains this sort of heat loss is effective waterproof clothing to stop rain, and other water, getting into your clothing. But it is not just about stopping water getting in; you must attempt to decrease the amount of sweat in your clothing. When you exert yourself, getting wet from the interior can be a more serious issue than water coming in from the exterior of your clothing. Breathable fabrics that permit perspiration to pass through and escape will provide help to an extent but if you’re working hard, you can still get sweaty and damp.
If you take notice of the environmental temperature and your level of exertion you may help to maintain an even body temperature and reduce sweat by adjusting layers, especially taking layers off before you start exercising. Ventilation also helps – open up front zips, reveal the neck, and so on. Adjust your clothing as necessary during exercise. You may control our activity level; if you’re still getting hot and sweaty in spite of the above measures then you must likely slow down a bit and. Pace yourself.
Respiration (breathing) : As you breathe in cold air it is warmed before it gets to your lungs. You then breathe out warm air and you are actually losing heat every time you breathe. There is nothing we are able to do about breathing. We’ve got to do it to stay alive! In comparison with the other mechanisms of heat loss , though, heat loss thru breathing is comparatively irrelevant.
Conclusion: So these are the 5 ways you lose heat to the environment in the wilderness: Radiation, convection, conduction, evaporation and respiration. If you understand these mechanisms well and mix this knowledge with your expereience of the outside, it should assist you in staying safe and less likely to suffer from hypothermia.
Paul Kirtley teaches bushcraft and survival skills. He is committed to nature, outdoor life and remote travel. This is something that comes across clearly on his bushcraft courses.