It’s easy to recognize feeling cold in the outdoors — shivering, for example. But how our bodies get that way isn’t as obvious.
4 Ways Bodies Lose (and Gain) Heat
Minson helped us understand how heat is lost. His tips offered insight into what to wear to stay warm this winter — and cool next summer. There are four ways the body loses heat: conduction, convection, evaporation, and radiation.
Conduction: Contact Between Objects
Conduction is direct molecular contact between two objects. That could be your butt and the snow when you’re sitting down in a pile of powder. If you’re one object, the other can be anything cold: snow, ice, even metal.
“Imagine the palms of your hands on your handlebars while riding in really cold conditions,” Minson said. “If you grab cold metal with your bare hands, you will lose a lot of heat to the metal.”
What to do about it: Try to avoid direct contact with cold surfaces and use low-compressible materials between your skin and cold surfaces when necessary.
“Some cycling and ski gloves have padded palms, which help to create an insulating border and reduce heat loss through conduction to bars or ski poles,” Minson said.
Climbers often carry a small piece of foam to sit or stand on when taking a rest break or brewing up their morning coffee on snow or a glacier. “Also, try putting your cold feet on someone’s stomach to help warm them up and possibly even prevent frostbite,” Minson said.
Convection: Moving Air or Water
Convection is losing heat through the movement of air or water molecules around your body. It works closely with evaporation (see below).
“If you are running on a very hot, humid day, you will lose a lot more heat if there’s a breeze across your skin than if not,” Minson said.
You can also lose heat through the convection of moving water. That’s why you get a lot colder standing in a stream than in a lake.
“You lose heat through conduction to the water, but convection moves the warmed water away from your body,” Minson said.
What to do about it: Stock up on windproof clothes for cold conditions. On the flip side, wear lighter, looser-fitting clothes for summer heat.
Evaporation: Liquid Sweat to Water Vapor
Ever get wet and not feel cold until a breeze hits you?
“Evaporation and convection work together to cool you,” Minson explained. “That can be nice when you pour water on your shirt while hiking but can suck if you just fell in a stream on a cold day while backcountry skiing.”
What’s weird is we lose heat through sweating only if the sweat evaporates. “Those pools of sweat below the stationary bike in spin class do nothing to cool you down,” Minson said.
Why? Because it takes energy to convert water into water vapor (i.e., evaporation). That energy comes from the heat produced in the muscles while exercising. This heat is carried to the skin via — you guessed it — convection of the blood from the muscle to skin.
The energy in that heat is then used to convert liquid sweat to water vapor (assuming the environment is dry enough). In humid, water-saturated air, we overheat because “the air can’t hold any more, so we can’t evaporate sweat, so we don’t lose the heat.”
What to do about it: Wear layers in the cold, but make sure you don’t get overheated.
“On a hike, climb, or cross-country ski tour, start a bit cold, as you will heat up quickly, and then try to avoid sweating very much,” Minson said. “If you are starting to noticeably sweat, lose a layer.”
As soon as you decrease activity, you’ll lose heat through evaporation and can quickly get quite chilled.
“Again, layering and having a very breathable but water-resistant outer material can make all the difference,” Minson said. “These materials are designed to keep water droplets out but allow water vapor to escape.”
Radiation: What We Get From the Sun
Last but not least is radiation, the loss (or gain) of heat through electromagnetic waves.
“This is how the sun heats you, and why 90 degrees can feel quite different on a sunny versus cloudy day,” Minson said.
But we lose heat by radiation mostly when we’re sedentary, sitting at our desks.
“It will be rainy and cold here tomorrow,” Minson said. “So I plan to put my feet up by the fire to take in the radiant heat and keep me comfortable while drinking my cold cider (insulated to keep it from getting warm through radiation).”
What to do about it: Materials like Columbia Omni-Heat Reflective and Omni-Shade, for example, can actually reflect electromagnetic waves. This sends them either back to you to keep you warm or away from you to cool you off.