By Kim O’Hare
Many people will be heading off for winter vacations soon. Whether your winter expedition involves skiing, snowboarding, trekking or even winter camping, they all have one think in common - a cold environment. Wearing the appropriate clothes to protect you from the cold can make the difference between a fun outing and an awful one. We’re not necessarily talking stylish, we talking functional, although the two are not necessarily exclusive.
Body activity produces heat. As activity increases or decreases heat production follows suit. You need to insulate the body to minimize heat loss. The insulation property of clothing depends on the dead air space next to the skin. The clothing isn’t keeping you warm, it’s the dead air. Wearing multiple layers of clothing keeps you war, because it creates multiple layers of dead air.
Why not just have lots of layers on and sweat? Heat loss from a wet surface can be up to 25 times greater than a dry surface. If you sweat, you will lose heat faster through evaporation. You also run the risk of dehydration increasing the risk of hypothermia. So you want to control your layers so as to be warm at the activity level you are in, but not sweating profusely. By continuously adjusting your layers you can keep comfortable. In order to properly insulate, you need to have an outer layer that is windproof.
Clothing which allows ventilation is also helpful. Controlling underarm and body openings allows you vent without having to actually remove a layer. Size matters! If clothes are too loose, the bellows action pumps warm air out through the openings. You need to have clothes that fit properly, but not tightly. Too tight, actually reduces dead air space and restricts body movement.
Another general rule: the efficiency of clothing is proportional to the size of the body part it covers. Thus insulation added to your torso will be more thermally efficient than the same thickness added to your arm or leg. It will also help maintain that body core temperature. This is why vests work well to maintain body heat.
It gets into some complicated physics, but tight thin gloves actually make your hands colder. Because they are tight there is no dead air, so what they are actually doing is increasing the surface area of your hands, thereby increasing heat loss. Gloves need to provide at least ¼ inch of insulation to be effective. Generally though you’re better off with mitts.
Wool is warm because the its kinky fibres provide a lot of dead air space. As much as 60-80 percent of wool cloth can actually be air. Also, wool can absorb a fair amount of moisture without imparting a damp feeling because the water “disappears” into the fibre’s spaces. Even with water in the fabric, wool still retains dead air space and will still insulate you. The disadvantage to wool is that it can absorb so much water it can get really heavy when wet. Wool releases moisture slowly, with minimum chilling effect. Tightly woven can be quite wind resistant. An advantage to wool is that it is relatively inexpensive However, it can be itchy against the skin and some people are allergic to it.
Synthetic pile or fleece has a similar insulating capacity as wool, holds less water and dries faster. Pile is manufactured in different weights offering different insulation value. The disadvantage of pile is that it has very poor wind resistance and hence a wind shell on top is almost always required.
Polypropylene and other hydrophobic fabrics offer dead air space and cannot absorb water. The fiber is hydrophobic so it moves the water vapor away from the body. Polypropylene layers are extremely effective if worn directly against the skin as a way of keeping the skin from being wet and reducing evaporative heat loss. As the water moves away from the body it evaporates, but each additional millimeter of distance between your skin and the evaporation process decreases the amount of body heat lost. Some fabrics rely on the chemical nature of the fiber to be hydrophobic. Others fabrics use a molecular coating to achieve the same end.
Another way to stay warm in the winter is through vapor barriers. The body is always losing water through the skin even when we are not active as long as the ambient humidity below 70 percent. A vapor barrier blocks the transportation of water vapor. When worn near the skin it keeps water vapor near the skin. Eventually the humidity level rises to the point where the body senses a high humidity level and shuts off perspiration. This prevents evaporative heat loss and slows dehydration. When you are active, like snowshoeing, and you are wearing a vapor barrier you must carefully monitor how you sweat.
Polarguard, Hollofil, Quallofil and others are synthetic fibers which are primarily used in sleeping bags and heavy outer garments like parkas. The fibers are fairly efficient at providing dead air space (though not nearly as efficient as down). Their advantages are that they do not absorb water and dry fairly quickly. The disadvantage is in their bulk, you end up looking like the Michelin Man.
Superthin fibers such as Primaloft, Microloft, Thinsulate and others are based on the idea that by making the fiber thinner you can increase the amount of dead air space between successive layers. Under laboratory conditions a given thickness of Thinsulate is almost twice as warm as the same thickness of down, however, the Thinsulate is 40% heavier. New materials such as Primaloft and Microloft are superthin fibres that are close to the weight of down for an equivalent fiber volume.
Down is a very efficient insulator, providing excellent dead air space for very little weight. The major problem with down is that it absorbs water. Once the feathers get wet they tend to clump, and lose dead air space. Down is very compressible, which is an advantage when putting it into your pack but also realize that your body weight compresses the feathers reducing the insulating quality.
Cotton is basically useless in winter since absorbs this moisture and the water occupies the space previously occupied by dead air. This means a loss in dead air space, high evaporative cooling, and a garment that is almost impossible to dry out.
The Body and Clothing
Because the head has a very high surface to volume ratio and the head is heavily vascularized, you can lose up to 70 percent of your body heat through your head. The adage - if your toes are cold, put on a hat - is true.
For your hands mitts are warmer that gloves because you don’t contend with the curvature problem described above. Also the fingers tend to keep each other warm, rather than being isolated as in gloves. Layering is also a good idea for you hands.
Finding the right footgear depends a great deal on the activity as well as temperature and environment. Most footwear contains the materials discussed above so it depends upon what characteristics suit your situation. Again keeping your feet dry is critical so in a damp environment you’ll need water proof or at least water resistant footwear. One of the best systems for keeping feet warm is using multiple layers in the form of socks. Start with a thin polypropylene liner sock next to the skin to wick moisture.
So as with anything else, read the labels carefully and do a bit of planning before setting off on your winter outing.