Cold Weather Clothing Part 1: How Heat Escapes Your Body

It is cold outside. Hitting negative digits last week, here in Ohio. Cold weather clothing  is the hot topic of the day. Plenty of opinions out there, good and bad. While I have a few recommendations, I think we really need to zoom out and take a look at the big picture how heat loss happens and by what mechanisms. This in turn, will help us make more informed decisions as we outfit ourselves.

Note: We are talking about cold weather clothing for people who are active and moving. Spending more than a couple hours out. Hiking, rucking, working, or perhaps more freedom fighter type activities. I am not talking to folks needing a simple heavy coat to move from warm structure to warm structure.

Heat Is Energy

Have you ever heard some variation of the phrase “the cold crept in”? Great word picture, but completely wrong when it comes to the actual science of how things work. Cold cannot move, since cold has no substance. Cold is simply the lack of heat. Cold air moving is simply air that lacks heat. Heat can move, however. Heat is a form of energy, often measured in BTU’s or calories. “Wait, calories? I thought that was a food term?” you might ask. Yup, it is. Food has a potential for energy and we measure that is Calories (1000 calories equal one capital “C” Calorie). But I digress.

Heat is energy. It can move. For the purposes of cold weather clothing (including sleeping bags/pads/etc.), we are putting energy into our body through food. Our body converts that into heat. That heat then does it’s very best to escape us through a variety of mechanisms. There are four primary mechanisms that we are worried about here: Conduction, Convection, Radiation, and Evaporation.

Heat Loss Mechanisms: 

Conduction: This is the transfer of heat energy through contact with a solid. Sit naked on a cold metal folding chair and you will experience conductive heat loss. We see this in play when we stand or lay directly on the cold ground, sit on a frozen log, or hold onto a cold metal object.

Convection: The transfer of heat from a surface by means of a “fluid” such as air. The cold (in this case) air, passing over a warm surface (your skin) and carrying away heat with it. Convection ovens work the same way, only cooking your food by blowing hot air across it.

Evaporation: When a liquid  turns into a vapor (gas), it takes heat energy with it, leaving the surface it occurred on cooler. Our body was designed to take advantage of this, producing sweat as a natural cooling mechanism when the body thinks we are going to overheat (HYPER-thermia).

Radiation: This is the movement of heat energy away from a heat source (your body) by means of electromagnetic radiation. When you shine your 1000+ lumen flashlight on your hand and it feels warm, that is a type of electromagnetic radiation we call light. Imagine your body is constantly radiating heat energy away from you in all directions. That is what is happening right now as you read this. 

What can we do about it?

Stay tuned for “Part 2: Solutions”, where I will dive into cold weather clothing systems and my recommendations.

See y’all around the fire,
Jayberry

 

Photo Credits: Padraig Croke