the next generation of smart fabrics while garment designers dream up innovative features. Clothing manufacturers crank out new lines so frequently that it isn’t possible to give you specific information on what’s available now, so here are some general guidelines to help you choose the best clothing for your trip.
REGULATING YOUR BODY TEMPERATURE
In order to plan the right clothing for a trip, you need to understand how your body reacts to the temperature and weather conditions you are likely to experience. Balancing the heat you are losing to the environment with the heat you generate from exercise and absorb from the environment is called thermoregulation. If you gain more heat than you lose, you experience a heat challenge. (See “Regulating Body Temperature,”.) If you lose more heat than you gain, you experience a cold challenge. The ability to regulate body temperature is critical for preventing hyperthermia and hypothermia. (See “Heat-Related Illnesses,” and “Hypothermia,”.)
One way to regulate body temperature is to wear the right clothing and layer your clothing properly. Clothing items should be versatile enough to meet the various seasonal and weather conditions you may encounter. Since each person’s body is different, experiment to determine your individual requirements.
How Your Body Loses Heat
Heat leaves your body in the following ways:
Conductive Heat Loss occurs when contact is made between your body and a cooler surface. It can be minimized by not sitting on the cold ground, especially on snow. Conduction occurs 25 times faster with wet clothing than with dry. Prevention: Thickness of insulation.
Convective Heat Loss occurs when your body heat warms the air adjacent to your body; that air then rises and moves away from your body and fresh colder air replaces it. Wind increases the speed of heat loss through convection. The impact of heat loss from convection is measured by the windchill factor. (See “Windchill Index,”.) This same process happens when you are submerged in cold water, but it happens much faster than in air because of the greater density of water. An important element in dressing for the outdoors is trapping the air around the body. Prevention: Windproof garments.
Radiant Heat Loss is caused by the escape of infrared radiation from the body. It is minimized by wearing insulative fabrics or those with reflective fabric that reflects the heat back to the body. Prevention: Thick layers of insulation or reflective material.
Evaporative Heat Loss occurs when perspiration (water) on the skin evaporates, drawing heat from the body. Changing water from a liquid to a gas takes a lot of energy. This is why sweating helps cool you off when you are hot. In hot weather, evaporation is essential in cooling your body down to prevent heat illnesses. (See “Heat Challenge,”.) However, when it’s cold you want to minimize the amount of sweating to reduce evaporative heat loss. Prevention: Fabrics that move water away from the skin and vapor barriers (page).
Trapping Your Body Heat
Clothing insulates you from the environment by trapping your body heat. The best insulation is a layer of static, unmoving air close to your body, known as “dead air.” This air is warmed by heat given off by your body (through radiation, conduction, and convection) and maintains a warm microclimate around your body. Clothing insulates by creating pockets of dead air. How much a particular clothing fabric insulates is based on its loft or thickness—the greater the loft, the more dead air space. Also, different fibers are better at creating dead air space than others. The goal is to find a fiber that creates lots of dead air space and at the same time doesn’t weigh very much. This is known as the warmth-to-weight ratio. A really light fiber like down has an excellent warmth-to-weight ratio.
Not all clothing is designed to insulate. In hot desert environments, thin layers of clothing with negligible loft are worn not to insulate but to provide shade from the sun to minimize overheating. You want something loose-fitting that ventilates and allows your sweat to evaporate, cooling you off.
By wearing multiple layers of different types of fabrics you can maintain a comfortable body temperature without excessive sweating (which can lead to heat loss). Throughout the day, you “layer up” or “layer down” as temperature conditions and/or activity levels change. By experimentation, you can determine which of the base layer, insulating layer, and shell layers you require in various situations. The layers should not restrict your movement and the outer layer, especially, should not be too tight, since tight outer layers squeeze the layers beneath and actually compress the dead air space in layers below, reducing their insulation value. You can modify one or all of the following factors to properly thermoregulate.
Clothing Layers The number and type of layers you wear allow you to create sufficient dead air space for insulation and protection from external conditions (wind, rain, etc.). Extra layers may be added in the cooler hours of the morning or evening, or when your activity level drops, like at a lunch break.
Activity Level Increasing or decreasing your activity level increases or decreases the heat you generate.
Staying Dry An important factor in retaining heat is to minimize wetness, since you can lose heat 25 times faster in wet clothing than in dry. Moisture comes internally from perspiration generated by exercise or externally from rain or snow. You want clothing layers that minimize the buildup of moisture close to your skin and also protect you from external moisture.
Ventilation Opening up or closing the layers of your clothing allows you to decrease or increase heat loss as needed, without having to actually remove or add a layer. As you move, a bellows action occurs in clothing that pumps your accumulated warm air out through openings and pulls the cooler air in. In some conditions, this bellows action can reduce your body’s insulation by 50 percent or more, so unzip if you are too hot and zip up if you are cold. Ventilating also prevents moisture buildup from perspiration. Look for clothing that allows for easy ventilation, such as full-zip outer shell jackets, armpit zippers in shell jackets, zip-front turtle-necks, button-down shirts, and side-zip pants. Rolling up sleeves and pants legs is another way to ventilate.
The Base/Wicking Layer
The base/wicking layer keeps the skin dry and comfortable. This layer transports moisture from body perspiration away from the skin to the outside of the fabric. This layer should dry quickly. In cool weather, wear close-fitting layers to provide insulation. In warm weather, wear loose-fitting layers to maximize ventilation and absorption of moisture for the skin to keep cool and dry. There are a number of different ways to wick moisture away from your body:
Hydrophobic/Hydrophilic Fibers These are synthetic fibers often made of polyester or polypropylene that do not absorb water (as cotton does). They are extremely effective worn directly against the skin to keep it dry and reduce evaporative heat loss. In addition to not absorbing water, many of these fabrics are hydrophobic (“water-hating”) on the inside, so they push the water vapor from the area of highest concentration (next to your skin) to the outside of the fabric. Some fabrics are hydrophilic (“water-loving”) on the outside and pull the water outward. Others are bicomponent and use
