There’s a reason the first principle of Leave No Trace is ‘Plan Ahead & Prepare’ – prevention is the key to pleasant and safe adventuring in the outdoors. Humans are terrifyingly susceptible to cold-related injuries such as hypothermia - the rapid, progressive mental and physical collapse caused by the core temperature of the body cooling to below 95°F. According to the CDC, hypothermia only requires mild temperatures of around 40°F to begin onset; particularly in wet, windy environments. Such conditions are known to be present in the mountains not just in winter but well into the ‘shoulder seasons’ and even into the summer months at higher elevations once night falls.

Excessive loss of body heat in the backcountry is not only uncomfortable, but can quickly lead to dangerous life-threatening conditions. This scenario generally occurs as a result of poor clothing quality, selection and/ or management. The rigors, constraints and dynamic nature of backcountry conditions demands a clothing system that is lightweight yet versatile, packable yet robust – sounds easy right? Don’t fret though, decades of research and real world testing (and mistakes) has brought us the fool-proof concept of layering systems. Such clothing systems allow simple transitions as weather, temperature, exertion level and other factors change throughout your adventure to maintain an optimal body temperature for comfort and safety.

I spoke with John Reyes and John Bulmer of Adirondack Mountain Rescue, a non-profit wilderness and technical search and rescue team based out of Clifton Park, NY. When I asked if they had any thoughts on the role of improper layering on initiation of rescue operations, they had a few thoughts to share. “Proper layering and temperature management are critical skills to master for anyone who spends time in the backcountry. The opportunity for people to find themselves in a situation where they are in danger of becoming hypothermic while being too far away from rescue is very real. In the wilderness many people fall victim to hypothermia, and to a lesser extent heat related medical conditions, every year. Being prepared and knowing how your own body reacts to insulation can keep you out of harm's way.”

The Science of Heat Loss

In order to understand how to properly implement a layering system, first we need to understand thermoregulation and how the body loses heat through evaporation, radiation, convection and conduction.

Evaporation occurs when energy, in the form of heat, is released during the process of water molecules converting into their vapor form. Evaporation as a result of sweating is the body’s primary means of releasing heat and poses a particular issue when overexertion causes ‘sweating out’ – soaking through your clothing due to excessive perspiration. This is due to the fact that water pulls heat away from the body about 25 times faster than air. Rain, snow and other forms of precipitation also facilitate excess evaporation when allowed to create trapped moisture against the skin. For these reasons, garments that effectively wick moisture away from the body are an essential part of the layering system.

Radiation primarily occurs from the head and core, as the cold air ‘steals’ the warmth of our body in an attempt to create temperature equilibrium. By layering garments together, warm pockets of air are readily created within our system that match the heat of the body and nullify the radiant effect.

Convection is most well recognized as wind chill factor and results from the movement of air and fluids. As air moves past the skin, it draws the body’s heat away with it and this effect is magnified with the speed of the movement. There’s a reason a wind gust on the summit can chill you to the bone so easily. A wind-proof layer can significantly reduce heat loss in this form.

Conduction works in a similar manner to radiation; contact with cold materials or surfaces such as rocks, ice and the ground or even cold raindrops causes heat to be drawn from the body to the colder material. The solution – an outer waterproof hard shell to create a durable barrier between you and the harsh outside world.

Building the System: The 3 W’s of Layering

Base Layer – Wick That Moisture

Your base layer is going to be your primary guard against evaporative cooling and should fit relatively snugly as it needs to lay directly against your skin to work most efficiently. It’s critical to select a base layer specifically designed for this purpose – polyester blends and merino wool are safe bets. Lightweight options will be most effective at pulling moisture away from the body and more breathable, while mid-weight options will provide an extra layer of warmth in harsher conditions. Heavy weight options are also available but generally are layered over a lighter layer that sits directly against the skin.

Mid/ Insulation Layer – Trapping Warmth

This layer is designed to draw moisture vapor away from the base layer to the outer shell, while at the same time trapping warm air against the body and is your primary defense against radiant cooling. Many people choose to pair a fleece layer with a down insulating layer. Fleece is a great option for your system as it is both breathable and retains warmth when wet. Insulating vests, coats and pants can consist of synthetic down or goose down. Synthetic down offers a more humane option as well as retaining its warmth properties when wet unlike goose down, however, it is slightly less compressible. I prefer vests versus full coat options for my upper insulating layers as it reduces weight/ bulk with minor reduction in warmth as less heat is stored and released in the arms than the torso. Fit is another important consideration for the mid layer. Garments must be loose enough to allow warm air to build up between layers and moisture to wick to the outer shell, but snug enough to prevent release of warm air.

Outer Shell – Guarding from the Weather

Minimizing cooling through conduction and convection, the outer layer is the armor of the system and acts to repel wind and precipitation while trapping precious body heat. You may hear outer layers referred to as ‘soft shells’ and ‘hard shells’. Soft shells consist of a weather-resistant but relatively breathable material with more give and a light layer of insulation. While hard shells are generally completely weatherproof but offer limited insulation or breathability unless vents are featured. These options can be worn independently or paired together, depending on the conditions present. Be sure to consider the bulk associated with your other layers when sizing your outer shell.

Managing the System

Even the most thought out composition of layers still don’t assure a comfortable adventure if those layers are not properly managed. Plan to follow the tried and true adage ‘be bold, start cold’ when selecting your starting layers by anticipating terrain and exertion level. This will help you avoid scrambling to strip layers ¼ mile down the trail to avoid sweating out.

In the best case scenario, full layers will rarely need to be added or removed mid adventure aside from throwing on a summit jacket if peak bagging is your game. As excess heat is generated, try making small tweaks rather than strip or add a full layer to see if a few degrees is all that is needed to bring you back to a comfortable temperature. Below are some options to consider;

Seek out hard shell options with built in vents, they will be pricier but worth the money for their versatility! This feature provides release of excess heat during exertion when harsh conditions prevent removal of the weatherproof layer.

Rather than removing your hat and risk losing an excess of heat, try flipping the edge of the hat up to expose only your ears.
The simple act of rolling up sleeves/ pant legs releases a surprising amount of heat.
Gaiters can also trap heat produced by the hard-working calves, removing (if conditions allow) or rolling them down can be an effective venting method.
Removing or putting a hood up can make a startling difference in overall body temperature.

Perfecting the System

Winter layering is both a science and an art form, don’t expect to get it right from the start! Many factors besides temperature can impact your layering system; humidity, wind speed, nutrition consumed, level of exertion and fatigue can all effect your body temperature and perspiration rate. Be patient with yourself and test out layering combinations on shorter/ less strenuous outings first to assure you understand how your body works with your system under various conditions.

I always keep an adventure journal and use it to note mileage, elevation, duration, weather conditions and layering combinations I found to be most comfortable as well as any other lessons learned. A weather-proof notepad and pen can be a good option for this. I’ve found this type of documentation to be invaluable over the years in helping me fine tune not only my layering system but my packing list and technical skills.

At some point, you WILL make a mistake but that’s okay as long as you learn from it! Anyone who tells you they’re an experienced outdoorsperson and they’ve never spent a day in the backcountry miserable and uncomfortable because of improper/ malfunctioning gear is either a liar or a mythical god. Sadly, I have yet to run into Zeus on the trails. The key is assuring those mistakes don’t lead to a dangerous situation requiring medical response.

Good luck and happy adventuring!

Thanks to our friends at Adirondack Mountain Rescue (AMR) for their expert contribution to this article. To find out more or donate to their cause, visit them at their website at; https://www.adirondackmountainrescue.org/ or follow them on Facebook at; https://www.facebook.com/adirondackmountainrescue/

Cold Weather Outdoor Layering: Consider the System