The science of garment layering.
Your clothing layers are your mobile environment. Within this mobile environment, there is a microclimate that you, “the active resident, " must control proactively.
To do this, you need to select layers carefully, considering your work rate and the likely weather and wind changes, given your planned route and altitude gain. All this without dials, buttons, physical controls, thermostats, or smartphone apps. Scary?
Garment layers are not and never can be a turnkey solution like buying and using a car. Cars are governed by masses of legislation, and you are required to pass an annual MOT test to drive one. The outdoors and mountains are largely legislation-free for you to enjoy and learn from your mistakes! Experience is what you gain after the first few times you really need it! Understanding basic science will accelerate your on-hill learning.
Fundamentally, when out in the wilds and without sun, the only source of warmth is food and drink! Your metabolism (marked ‘M’ in the diagram) is the mechanism whereby food and drink are converted to glycogen to power your muscles and heat. Activity work rate determines how well this heat is moved around your body by blood circulation.
However, metabolism only functions within a narrow range of temperatures. If your core temperature drops, your hypothalamus (see diagram) actuates vasoconstriction, and your hands and feet go cold. Hence, Granny’s old advice, ‘If your hands are cold, put your hat on,’ is technically correct. Hypothermia is when your core temperature has dropped to the level at which you cannot metabolise food and drink.
Garments provide the means of controlling heat loss. Our graphic shows the many different types and areas and contact points of heat loss or gain you have to deal with to be able to make your ‘mobile environment’ a comfortable place, almost regardless of external conditions.
Heat losses occur: see diagram.
By conduction, where surfaces touch.
By convection, a little when you move within your garments but mainly by wind. (The weather forecasters take wind speeds into account when giving temperatures by saying ‘feels like’, which is technically known as the wind-chill factor.)
By respiration through your mouth and nose.
By sweating, which causes evaporative cooling.
By radiation, but this is usually small.
For more information, read our book Keeping Dry and Staying Warm, see see chapter 3.1
See also section #4 Garment layers for cold and high altitude.
IN THE DIAGRAM BELOW, 5 key actions, both passive and active, occur.
All 5 require skills based on an understanding of fitness and human physiology, nutrition, 24-hour temperature and weather fluctuations, clothing choice and, most critically, how to use the layers of your choice. Carrying out all aspects well is a high skill level, which we call PERFORMANCE LAYERING.
