Hiking in the winter challenges you in many ways. Maintaining thermal homeostasis is critical to health and survival. Humans can cope with and exercise in harsh conditions despite extremely low temperatures when properly prepared. However, when not ready, the winter backcountry traveler is at elevated risk for cold-related injuries, including hypothermia, frostbite, and musculoskeletal trauma. In some cases, death is the result of unpreparedness during winter hiking.
A system for survival
Your winter gear list is not a list but is instead a system for survival. Each component is used to keep you safe and healthy while hiking in extreme conditions. The items you bring all have a purpose, and some may have several. In any case, during the winter, each article should be related to keeping you healthy and alive FOR MORE THAN THE DURATION OF YOUR EXPECTED OUTING. You should have enough insulation for the coldest possible temperatures you may experience, including an overnight in the woods.
Clothing and insulation
Your clothing has one primary purpose in winter hiking, to prevent cold injury. With that said, the amount of clothing, type of clothing, fit of clothing, AND use of clothing all play a factor in its ability to do that. Clothing helps maintain body core temperature by slowing conductive and convective heat loss in cold environments.
Clothing insulation units (Clo units) measure how well an article of clothing protects against cold (heat loss). For example, at a resting state (Oxygen consumption of 3.5 ml/kg/min), with no wind, a person can maintain core temperature at 21℃ (68.8℉) with clothing of 1 Clo unit. During sleep, where body core temperature drops (2.8 ml/kg/min), the Clo needed to maintain core temperature at 0℃, -20℃, and -50℃ is 6.7, 10.6, and 15.5, respectively. This changes with exercise. During heavy exertion (21 ml/kg/min) again at 0℃, -20℃, and -50℃, Clo needed to maintain core temperature is 1.0, 1.6, and 2.2 respectively.
We can see that at 0℃, it takes 6.7 times the Clo to maintain body core during sleep vs. heavy exertion. In other words, if you get stuck out in the woods at night and the daytime temperature was 0℃, and it dropped to -20℃, you would need about 6.5 times the insulative value of your clothes used during activity when hiking to keep warm at rest. The above is all based on NO disturbance of the microclimate that your insulation provides.
There are six factors that can affect Clo value of clothing:
- Wind speed will disrupt the zone of insulation.
- Body movements will disrupt the zone of insulation by pumping action of the arms and legs.
- Chimney effect will disrupt the zone of insulation due to loose-fitting clothing. Poor fit that allows too much space will allow trapped air to ventilate away from the body.
- Bellows effect is caused by vigorous body movements and ventilates warmed air away from the body.
- Water vapor transfer can be blocked which decreases heat loss by evaporative cooling.
- Permeation efficiency factor is a measure of how well an article of clothing absorbs and wicks moisture away from the body thus reducing cooling and conserving heat.
The best way to retain heat with clothing is by using several lighter layers of clothes than one thicker layer. The ability for clothes (or sleeping bags) to insulate is based on its fiber’s ability to trap warmed air. At night, your sleeping bag doesn’t warm you; you warm the sleeping bag. Thus the same thing applies to your garments. Wearing several layers allows for clothing to have a greater ability to trap air and form a warm microenvironment that helps maintain core temperature. Changing the number of layers with levels of exertion is key. This is an important concept; manage layers as you go. Start your hike with a chill as your body will increase your body’s core temperature as soon as you begin to hike. Your initial chill will go away quickly. As you progress and temperatures or wind speed changes or if you take a break, add or subtract layers as needed.
3 layer system +1
Base or skin layer
The relatively light skin layer should be a wicking layer allowing the garment to wick moisture away from the skin and dry quickly. A base layer’s ability to wick moisture and dry quickly helps the hiker manage body temperature while maintaining a level of insulative value. Wet garments lose up to 90% of their insulative value. Cotton absorbs moisture well, but the fibers do not wick the moisture away; instead collapse and retain it. The term “Cotton Cools” comes from this fact, in winter or even cool summer conditions, “Cotton Kills” as it loses insulative value when wet. Given that cotton kills, this base-layer should be made from polypropylene. Bring AT LEAST 2 (or more) base-layers.
The mid-layer is generally a bit thicker but still provides a wicking factor that removes moisture from the base layer. This layer is made from some form of polypropylene or made from wool.
Above: Top light base layer and mid-layer, bottoms base-layer on top of waterproof/breathable bib, waterproof gloves, synthetic winter cap that can be pulled down below ears, upper right: green windproof fleece with hood, upper left: yellow GoreTex outer shell.
An outer layer can be a windproof fleece that insulates but protects from the wind. This wind protection is critical as air movement is one factor that affects the insulating value of clothing. The shell is generally a waterproof/breathable garment that protects from snow or other moisture sources from wetting your outer, mid, or base layers. A shell may be used even when no precipitation is falling but rather to protect you from blowing snow or moisture on trees rubbing against you as you hike, for example. The one main problem of hiking with a waterproof/breathable garment is that the “breathability” is always limited. Having pit zips or even just unzipping the front zipper will help vent some unwanted sweat/vapor. We have found the bib is better than pants for lower body protection and warmth—the bib strapping and coverage above the waist to the lower chest aids in heat retention at the torso.
The plus 1 – Heavy outer-layer
An outer insulating layer is a garment that is used during extended breaks or at a camp. It may be a parka-type coat that provides excellent warmth during extended times of inactivity. The insulation can be made from synthetic fibers or down. Even though down insulation loses its insulating value when wet, there are some down products on the market today that stand up better to moisture.
It has been estimated that up to 40% of heat loss occurs from the head, even though it only accounts for 8% of the body surface. A wool or synthetic winter cap will help slow this loss. Any cap should have the ability to cover the ears as they are susceptible to frostbite (the nose is also susceptible to frostbite). Bring AT LEAST 2 hats. For your nose and cheeks, try a neck gaiter, scarf, or face mask. If you are ascending above the treeline, use a balaclava that covers your nose.
Fingers and toes are at risk for frostbite in the winter. In our opinion using wool or synthetic gloves/mittens with a waterproof shell makes the most sense. You should bring AT LEAST 2 pairs of gloves with you on day hikes. Cold and sluggish fingers make everything more problematic in the winter woods.
If you’re going to invest tons of money, do it for your feet. Don’t rely on your summer boots. Cold, numb feet are not only painful; they can be deadly. Once your feet have succumbed to winter conditions, it’s like getting flat tires; you can’t get very far – fast. Investing in insulated winter boots that are made for hiking is key to your comfort and survival. Spending a few hundred dollars will make your winter outings enjoyable. They need to be insulated and waterproof as you’ll spend your day in a cold, snowy environment that can soak nonwaterproof boots. Insulation is key as the non-insulated boot will eventually fail in the cold snow. Winter boots that have high tongue gussets and are above the ankle aid in keeping snow out. The ideal boots should have rubber soles with aggressive treads that offer traction on ice and snow. Some boots have attachment points for secure snowshoe attachment.
Winter socks are essential also. A base layer sock with a mid-weight (or more) over sock made from wool or synthetic materials works well. Don’t go too heavy on the socks as it may cause blisters and restrict blood circulation. Remember, your feet will swell a bit as you hike so that a snug-fitting sock may get tight. We bring AT LEAST 2 pairs of socks on day hikes.
Finally, gaiters can be worn to stop snow and water from entering and soaking the inside of your boot.
Yes, your eyes need help in the winter. Blowing snow always seems to find a way into your eyes. The bright sun reflecting off the snow can impact your vision due to photokeratitis that may cause eye pain, blurred vision, headaches, and even temporary blindness. Using ski goggles or sunglasses will help alleviate this.
Backwoods wanderer with a passion for backpacking, hiking, and exploring the wilds of the Catskills and Adirondacks in New York. A Catskill 3500 Club Member and Adirondack Forty-Sixer. Climbed Mount Rainier. Professionally an Exercise Physiologist.