Properties of Cold Weather Hiking Clothing
The winter’s coming and it’s again that time of the year when every outdoor enthusiast should be prepared for the challenges of cold weather. It’s true that winter conditions vary in different parts of the world, however, one thing is valid always and everywhere and it does never change - you need warm, comfortable, and reliable hiking clothing in order to be able to explore nature in cold conditions. The main function of your apparel is to provide adequate protection against the cold during winter seasons. Cold alone can be, directly, dangerous enough not only for your health but for your life as well.
Cold weather apparel has many properties but insulation and breathability stand out as probably the most important properties of hiking clothing for cold weather protection. Insulation must ensure protection against the cold while allowing transmission of perspiration from the skin to the environment at the same time.
Your comfort in cold weather depends largely on the balance between thermal insulation and breathability because they determine the amount of heat and moisture that could be exchanged between the human body and the environment. The aim is that, through heat exchange between your body and the environment, your skin stays warm and dry. That’s a very important factor for your comfort, especially given your activity level and environmental conditions such as temperature and wind.
What do you need to know about hiking clothing for cold weather?
Heat loss during hiking in a cold environment
The human body maintains a stable internal body temperature thus heat production from the body should ideally equal heat loss. However, you lose more body heat than normal in a cold environment. This is determined by four environmental factors: air temperature, wind speed, relative humidity, and mean radiant temperature.
The metabolic rate varies from 80W to 1000W depending on the intensity of different activities. A huge part of this power (up to 85%) is converted into heat and some of this heat may have to be released to the environment so that you don’t overheat. At low activity levels, your body produces less heat thus it needs more insulation to achieve heat balance. Conversely, at high activity levels, your body produces more metabolic heat than needed, thus you have to reduce the insulation layer.
The table below shows metabolic energy production associated with various sports and activities. The metabolic energy production for a standard person while hiking is between moderate and high depending on the person’s average velocity. This explains, at least partially, the fact why in similar weather conditions on different occasions our bodies may or may not produce excessive amounts of sweat on the trail.
Table 1: Metabolic energy production associated with different types of sports and activities (values refer to a standard person with 1.8m² body surface area)
Source: Textiles in Sports*, p.265
The main mechanisms of the heat loss are the following:
In hiking, convection occurs between a backpacker and air or water in contact with him as the contact with warm air warms him up while the contact with cold air cools the hiker. The easiest way for an outdoor enthusiast to adjust the amount of heat loss is by zipping or unzipping his jacket. Convective heat transfer is largely affected by the presence of wind and water. Wind and especially wind speed strongly affect this process and increase convection. Additionally, garment features such as fit and design can have a significant impact on convective heat loss.
Radiation is the transfer of energy from warm to a cold surface through electromagnetic radiation. The impact of this type of heat loss is much less significant in comparison to the heat loss from convection, evaporation, and conduction because the only major consideration is the radiation that comes from the sun. Be careful about high radiative heating levels while hiking at an altitude, especially when there’s a lot of snow around because of the reflective nature of the snow. Your clothes can help you minimize the radiative heat transfer.
Conductive heat transfer occurs when two surfaces with different temperatures are in direct contact with each other. Heat flows through direct transfer of energy from the surface with higher temperature to the surface with lower temperature. This means that a standing or moving person isn’t affected the same way as a seated person. The direct contact between the former and the cold region (when hiking in cold environments) is limited to the contact between his soles and the surface, while the contact between someone who is sitting or lying on the ground and the cold surface is much more significant. Also, note that in gasses the mechanism of conduction is a bit different than the one in solid objects because their molecules are widely spaced and not adjacent so they rely on diffusion and collision to pass on the energy. This explains the insulating properties of down feathers and why hiking clothes rely on trapped air for increased thermal insulation.
One of the cooling mechanisms used by the human body utilizes evaporation of sweat from the skin surface. This way, the body can eliminate significant amounts of heat. The process is the following: sweat is spread across the skin surface where it changes from liquid to gas. It is then evaporated to the environment. An effective evaporative heat transfer includes a moisture-wicking base layer that spreads perspiration uniformly across a large surface at the skin and an outer layer that is “breathable” and can release the water vapor to the environment while minimizing condensation on the inside at the same time. Sweat evaporation may be required only at high levels of metabolic heat production in a cold environment. If you sweat excessively in such conditions, you need to get rid of the perspiration somehow. It can happen either by evaporation through your apparel or by convection through openings in the clothing.
We should add airway heat exchange to these four environmental factors. During breathing in cold temperatures your airways cool down and add to the skin heat losses. The airway heat losses can reach 15-20% of the total metabolic heat production depending on the air temperature - the lower the temperature, the more heat you lose. You can reduce this amount by using cover(s) for your mouth and nose.
Cold stress and wind
Cold stress is based on the fact that at low temperatures the body cannot preserve heat balance. In such cases, the heat loss exceeds the heat production and body temperature decreases. For example, heat loss doubles at 5°C compared to 20°C. At -10°C it goes down further, while at -25°C the heat loss is four times higher compared to 20°C.
The presence or absence of wind is another major factor concerning skin cooling and heat loss. Wind can be very dangerous because it accelerates heat loss from a warm surface. For example, the wind may penetrate your clothing (especially if it’s air permeable) and increase the convective heat loss within the garment causing excessive cooling and hypothermia. Hence, when planning trekking in cold environments, you need to add a windproof outer layer to your hiking outfit in order to be able to minimize excessive cooling of the body on the trail. Even if not fully windproof, the outer garment of your layered clothing system should be at least with low air permeability.
Influence of snow, rain, and moisture
Snow and rain also affect heat exchange in various ways but mainly by interaction with your clothing. Hence, you can prevent wetting from the outside by selecting a waterproof or water-repellent outer layer.
Getting wet from the inside is no less dangerous than getting wet from the outside. This usually happens from absorption and accumulation of moisture in your clothing. Keep in mind that this usually happens at high activity levels when your body produces and releases more heat and, in turn, sweats to cool down. Hence, in cold conditions, you need not only windproof and water-repellent or waterproof hiking apparel but also clothing that allows the passage of water vapor the so-called “breathability”. Inexperienced hikers often neglect the production of moisture of the body and its transportation through the layers. The truth is that they underestimate sweating in cold conditions because too few people really talk about that. However, the condensation of water vapor and its accumulation within the clothing determine the thermal insulation of the outfit. We’ve already mentioned in previous posts that moisture build-up inside your clothing reduces its thermal insulation abilities. But do you know how much exactly?
Table 2: Actual evaporation and difference in total thermal insulation as result of sweating and sweat accumulation
Source: Textiles in Sports, p.275
Table 2 shows an experiment conducted for three hours with a manikin at two sweating rates 100 and 200g/h/m² at temperatures between 0 and -40°C. The table shows that sweat evaporation is significantly reduced in the cold. Moreover, the thermal insulation abilities of the clothing are seriously reduced as a result of sweating and wetting the clothing from the inside as the reduction reaches nearly 30% at sweating rate of 200g/h/m² at -25°C.
During any physical activity (especially during high-intensity pursuits), you sweat and the production of perspiration depends on the core (dominant factor) and the mean skin temperature (secondary factor). You start sweating not immediately after you start working, exercising or doing an activity but only when your core temperature increases due to muscle activity. Similarly, the process doesn’t cease when you stop exercising. This is very dangerous because during activities such as cold weather hiking your clothing may get wet at the beginning of a break causing the so-called post-exercise chill.
If you wear heavy insulating clothing in very cold conditions, it is possible that moisture builds up into your outfit as it cannot be transferred to the outside. In this case, your heavy insulation will act as a barrier for the water vapor and as a result, it will condense inside your clothing, which can reduce the insulation by 30-50%. Hence, you need to find a balance between insulation and water vapor permeability of your hiking outfit.
Apparel requirements for cold protection
For cold weather, many experienced hikers and mountaineers use layered clothing system consisting of three, four or more layers of clothing worn one over the other. The main purpose for doing this is to get protection from the environment and to feel comfortable enough at the same time. The concept of layering allows the wearer to adjust the insulation according to his needs and preferences. For example, during heavy workloads, you can remove a layer to facilitate moisture transfer from the skin to the outer side of the clothing. Moreover, it offers better insulation because it can trap more still air between the separate layers.
The classic layered clothing system comprises of three layers: base layer next to the skin, insulating mid layer, and breathable outer layer that protects from rain and wind.
Base layer’s main functions are to be comfortable next to the skin, to provide adequate moisture management and to dry fast. This is achieved through an adequate level of breathability and wicking.
Mid layer’s main function is to provide insulation. Additionally, it should be lightweight and breathable.
Outer layer’s main functions are to shield you from precipitation, including rain, snow, and sleet, to retain heat, and to manage moisture.
See our post about hiking apparel layering for more information about layering.
Layering for cold weather hiking has many interesting properties and advantages compared to one thick-layered clothing system. For example, if condensation and freezing occur within the layered system, it often happens between the layers where it’s much easier to be removed and not within the material. It also provides the flexibility necessary to overcome the harmful effects of cold temperatures, especially during high-intense activity when your body produces up to 10 times more heat than normal. In order to achieve a heat balance, donning or doffing a garment should be easily done if necessary.
Using an integral layered clothing system allows your garments to trap air between the layers for better thermal insulation. Of course, different clothing systems have different properties, pros, and cons, though there are some universal hiking apparel requirements for cold protection. They are the following:
The clothing for cold conditions has to provide sufficient thermal insulation in every climatic condition even in the presence of strong wind. This presents a major challenge to your clothing for cold protection.
Excellent moisture management
Effective wicking, transportation, and evaporation of sweat from your skin to the environment are main requirements for your clothing because the presence of moisture inside your clothes is uncomfortable and will negatively impact the insulation as the thermal conductivity of water is approximately 24 times that of the conductivity of the air.
Protection from the elements
In foul weather, you need to be well protected from rain and snow and that’s the main role of the outer layer of the layered clothing system. The waterproof breathable garments work reasonably well in temperate and warm climates, however, these fabrics become less efficient in prolonged cold and wet conditions. The reason is that the membrane that protects you from precipitation can easily get clogged with dirt and sweat, which makes it much less efficient sometimes even useless. Anyway, in order to offer an optimal protection against cold, your hiking apparel has to be waterproof, windproof and breathable.
Adaptability to changes
Hiking outfit suitable for low temperatures is different than clothing for cold protection. The reason is that the former must be versatile - it should provide not only insulation but it should also be adjustable to the activity of the wearer and the weather conditions, while the latter often provides just high insulation i.e. it’s perfect only for low-level activities and doesn’t adapt to the wearer’s changes in activity levels or to changes in the environmental conditions. For instance, garment suitable for hiking in cold and mild conditions has to be very breathable, i.e. to be able to transfer a lot of moisture from the skin to the surface of the garment and from there to the environment.
Without a doubt, apart from offering optimal cold protection, the hiking outfit for cold weather should offer the best comfort possible. To maintain comfort, it should be easy to add, remove or adjust items effortlessly and efficiently according to own preferences and changes in weather conditions without impacting on activity. These include jackets, hats, and gloves and mittens.
Cold is a hazard to human health and may be very harmful to your physical well-being or work performance. Hiking is associated with high levels of metabolic heat production so it’s important to adjust clothing in such a way as to feel comfortable and avoid excessive sweating that may build up inside your clothing and aggravate its insulation capacity. In short, when hiking at low temperatures, your clothing has to maintain heat balance through proper thermal insulation and adequate moisture management.
The cold weather apparel for hiking should provide cold protection at low and high activity level. Moreover, when necessary and according to your needs, it should allow heat and moisture dissipation or heat retention. The best way is to build a hiking layered system consisting of several layers of garments with specific roles and functions. In addition to carrying out their individual tasks, these garments have to work together as one system.
Finally, there is no all-purpose garment suitable for all activities in all-weather conditions no matter what the manufacturers, dealers, and retailers say. Remembering that will help you stay skeptical about what you read or hear about a particular garment and its characteristics.
* In R. Shishoo (Ed.), Textiles in Sports, 2005, Woodhead Publishing Limited and CRC Press LLC