On the last few rescues, a very distinct chill has been in the air. I’ve learned through hard experience that the essence of staying safely warm in the winter wilderness is having proper clothing layers and knowing how to use them effectively.
Here’s some info to help keep you toasty while hiking this winter.
- Why are some materials warmer than others?
It’s all in the air. Clothing helps hold “dead air” against your skin. The body heats this dead air which creates a layer of warmth within the covered area.
The actual insulating value of your clothing is due to the thickness of dead air space it can hold. Your body is the true heat source. The clothing layers only serve to trap the heat and slow down your heat loss to the cold environment.
- So what are the best ways to save this “dead air”?
Choose the right layers. The key to staying toasty is having a number of versatile layers of clothing, which provide an appropriate amount of dead air space.
Each layer should have unique properties to hold, protect and allow you to adjust your temperature as necessary.
Importantly, cotton fabric should be avoided. During the winter cotton is downright deadly. It loses all its dead air when wet; thus its insulating properties disappear. Wet cotton is worse than dry bare skin and will rapidly suck the warmth from your body.
Polypropylene or other synthetic fabrics make for a good base layer. Keep your body in a snug (not tight) synthetic layer designed to wick moisture away from your skin. Synthetic fibers such as polypropylene don’t hold water, so your sweat is driven outward beyond the synthetic layer and away from your skin. This prevents evaporative cooling and creates a thin protective layer of warm air.
Wear wool, it’s a good warming tool. Wool’s insulating ability comes from the elastic, wavy crimp in its shape, which traps air between fibers. Depending on texture and thickness, as much as 60 to 80 percent of wool cloth can be air. Because the water “disappears” into these fiber spaces, wool absorbs a large amount of moisture while still keeping enough dead air space to keep you warm. Although fleece is not as versatile, it is still an acceptable option as well.
Down jackets are valuable. Lightweight and highly compressible, down feathers are very efficient insulators. They provide excellent dead air space for very little weight.
Unfortunately, if the feathers get wet they clump, lose dead air space and all their insulating power. Keep your down safely wrapped in a waterproof bag until you need it.
The outer shell should be wind and waterproof. It is essential to have an outer layer that is wind and waterproof while still able to ventilate and to allow excess heat and sweat to escape. Gore-tex and other similar fabrics are good options. Having underarm (pit) zippers on jackets greatly increases your ability to ventilate.
- The correct fit is important.
Right size clothing is critical. Layers that are too tight will constrict the body’s circulation which delays the time to warm up. You will especially experience this delay in your extremities. Tightness will also compress your clothing and actually reduce dead air space, which decrease your insulation volume.
But the opposite is also a danger. If it fits too loosely, your clothing will act as a bellow and actually blow out warm air and suck in cold.
- Protect your fingers and head too.
Your hands will appreciate mittens. Ever notice your hands feel colder after putting on a thin pair of gloves?
It’s physics, baby! When a thin layer of insulation is wrapped around a small diameter curved surface (finger), it increases the surface area and can actually increase heat loss until a thickness of about 1/4 inch. Thus, good motivation to bring backup mittens (which get around this problem by combining finger pockets) for extra-cold conditions.
And for your head, hats are essential in winter travel. The head has a very high surface to volume ratio and is heavily vascularized, so you can lose a great deal of heat without headgear. A balaclava or facemask may be required if it is windy to prevent facial frostbite.
- If you lose the dead air, what to do?
Have a dry backup and use it. Always have a dry backup of critical clothing and don’t wait too long to change into it after you stop moving. Heat loss from a wet surface can be up to 25 times quicker than a dry one.
I’ve hiked with a person who forgot this cardinal rule. She went to bed too exhausted to take off her wet socks. She woke up with toes permanently damaged from frost-bite.
Thanks to my good buddy and RMRU member Les Walker for the inspiration for this article. Have a great winter, and stay toasty!