The Fundamentals of Insulation

For a sleeping bag, the ideal insulation demands is not the same as that for clothing. This is because when you sleep your body remains at approximately the same body temperature and hence a constant metabolic rate.

Insulation in clothing has to meet demands of radical metabolic changes as you rest and exert yourself in the course of a hiking trip.

This means that your clothing has to be able to keep all the warm air in when you’re still and allow the heat to escape when you’re active.

So the important thing about keeping warm is not trying to keep as warm as possible but about regulating heat.

Achieving this heat balance may require conflicting tasks to be done at the same time and this means different layers of clothing.

Each layer does its job in keeping you both warm and dry. One layer wicks away sweat, another keeps the warm air trapped and one more protects you from the rain.

4 Kinds of Heat Loss = 4 Kinds of Barrier

The process of heat regulation is further complicated by the four different kinds of heat loss which means there needs to be at least four barriers.

Convective Heat Loss
This heat loss occurs when there is a transfer of heat from the body to air. The heat is taken away by the moving air (or water). This accounts for the majority of the body’s heat loss under normal circumstances.

To prevent this from happening, the best thing to do is to surround yourself with a layer of dead air. Air is an excellent insulator of heat.

The barrier should therefore be something that could trap air really well like down in sleeping bags, synthetics, wool, Thinsulate and others.

Evaporative Heat Loss
When the moisture on your skin turns into vapor, a huge amount of heat is lost. This is when you experience a sudden chill or some may call it exercise chill.

Sweat is nature’s way of cooling us down but sweat becomes undesirable, even dangerous, when you stop producing heat and your clothes are soaked.

To prevent this from happening your clothing needs to be able to wick away the sweat before it vaporizes.

Conductive Heat Loss
The is the direct way of heat. You lose heat when you are in contact with a stationary medium such as air, water, fabric that is at a lower temperature. Even so conductive heat is generally minor except when you fall into a freezing lake where conduction plays the biggest role in heat loss.

Radiant Heat Loss
The way the earth is heated by the sun is through radiation. This means that heat is transferred without any medium i.e. the sun doesn’t need to heat up the air to heat up the earth.

In the human body radiant heat loss is usually minor. When hiking, radiant heat does not usually occur directly from the skin but from the fabric next to it.

Reflective barriers are effective in prevent radiant heat loss.

No one material can be a barrier to all the heat loss channel. A down sleeping bag would do great for sleeping when your body temperature doesn't change dramatically but if you were to use the materials made for down bags on hiking clothing it probably won't be practical.