Wild Things, LLC
Successful Dressing for Cold Weather
Contributors
Dawn Dugan, Eileen Mockus, Edward Schmults, Dr. Michael Thornton, USN (SEAL)

 

Dressing for Cold Weather
 
Whether you are in training, on a special operation, or keeping our cities and towns safe for our citizens, you have bigger things to think about than whether you are warm, dry, and comfortable. Unfortunately, the weather doesn’t always cooperate or take this into consideration. In addition, most military and law enforcement personnel can’t choose the environment in which they are working, or the intensity of operations.
 
            If you live or work in areas that are mountainous, coastal, snowy, wet, unpredictable and less temperate, dressing correctly is key not only to your health and comfort, but also has an impact on your ability to complete your duties. While severe and varying cold weather climate conditions can affect operations, problems associated with the cold can typically be overcome with the correct training and clothing. With the right knowledge, you can choose cold weather gear that will keep you safe, warm, dry, and comfortable, allowing you to perform at your mental and physical best.
 
            Dressing for the cold weather is part art, part science. For the past 30 years, nWild Things has made technical clothing for the world’s most demanding users: high-altitude climbers and mountaineers, polar explorers, Iditarod participants, kite skiers and other fringe outdoor enthusiasts, and U.S. Military and law enforcement personnel.
 
            There is plenty of information on cold-weather dressing for the outdoor enthusiast. After all, if you are climbing K2, wearing the right clothing can be a matter of life and death. The same can be said for those in the military and in law enforcement, but in their case, the safety and lives of others are often riding on their performance. Yet, when it came to information geared specifically toward the U.S. Military and law enforcement, Wild Things noticed a significant lack.
 
            This manual is the first of its kind, and is designed to supply the information and knowledge U.S. Military and law enforcement personnel need to choose the right cold-weather clothing for their elite, demanding jobs. The purpose of this guide is not to sell our specific products, but to educate and inform so the right questions are asked, and the right choices are made.
 
            We encourage readers to contact us if, after reading this manual, they have additional questions or if they want to make edits or improvements. Just as our products are constantly being refined and upgraded, we would like this guide to be a fluid work. If you can make comments or relate experiences that illustrate a point please send them to us. If you can make a significant contribution we will send you some free stuff to show our appreciation. Let’s get started.
 
Part I: Environmental Influences
The Physical Laws of Nature
The physical laws of nature can be bent to our commands, but they can never be ignored. This is particularly true when it comes to our survival in the environment. A warm-blooded mammal, such as man, is scientifically termed a “homeotherm.” A homeotherm is an organism that must maintain its body temperature within a narrow range (96° to 101°F or 35.5° to 38°C) to properly function. The organism internally generates heat to accomplish this. The environment can both aid and hinder this by adding or removing heat.
 
            It is within this range that the body enzyme systems work the most efficiently. A wider range can be tolerated, but decreased efficiency of the vital processes in the body result. At the extreme ends of the tolerable range, death results from the inactivation and destruction of the inter-connected enzymatic functions.
 
            An environmental or ambient temperature of lower than 77°F (25°C) results in a lowering of the core temperature of a naked human, unless either a mental or physiological response to counter that drop occurs.
 
            The behavioral aspects of preventing core temperature drop is the essence of outdoor survival technique. Indeed, it can be complex. There are many ideas on proper insulation, new development of materials, and basically divergent concepts such as “breathability” and “vapor barrier” that can be studied from a physiological viewpoint. But there can be little doubt that the behavioral aspect of protecting our thin skin from the diversity of environments surrounding us is the most important aspect of enabling us to survive in any but a tropic environment. The migration of man from this point of origin necessitated his advance mentally to the level where tools are clothing could be made. Once our nakedness was covered, we could start to explore our globe and hope to survive the environments that we would encounter.
 
            The environment methods of heat transfer basically include conduction, convection, radiation, evaporation, and respiration. Variations of these basic physical events are: loss through the physiology of respiration and bellows effect of clothing and sleeping bags.
 
Conduction
The transfer of energy within and between bodies of matter, due to a temperature gradient. Heat spontaneously tends to flow from a body at a higher temperature to a body at a lower temperature.
 
            Cold weather travelers tend to lose more body heat this way because they often carry metal tools such as a ax, saw, or shovel, and they often rest by sitting on ice, snow or cold rock. Climbing ungloved over cold rocks or handling weapons is another mechanism of heat loss through conduction.
 
Convection
Convection is an active avenue of body heat escape in the outdoors. By radiation, the body continuously warms a thin layer of air next to the skin to a temperature nearly equal to that of the skin. If our clothing retains this warm-air layer close to the body, you remain warm. However, if this warm layer of air is constantly being removed by a brisk wind (convection), you feel cool and have to put on more clothing.
 
            In short, the primary function of clothing is to retain a layer of warm air close to your body. In conditions of sever cold and wind, you need garments of high wind resistance and insulating qualities.
 
Radiation
Radiation is a leading cause of heat loss in almost any situation. The head is the most efficient part of the body’s radiator system. So rapid is the radiation from your head in a cold situation that heat loss from an unprotected, uncovered head can be enormous. An unprotected head may lose up to half of the body’s total heat production at 40°F degrees, and up to three-quarters of total body heat production at 5°F degrees. Remember the maxim, “When your feet are cold, put on your hat.” Parkas with attached hoods are essential for protection against this dramatic heat loss in cold, windy, or wet situations
 
Evaporation
The process by which any substance is converted from a liquid state into, and carried off in, vapor.
 
            The evaporation of sweat from the skin and the insensible evaporation of water from the skin and lungs account for a substantial loss of body heat. There is very little you can do to prevent this loss. In fact, those in the outdoors are well-advised to help the process of evaporation by wearing fabrics that “breathe.” If water vapor cannot pass freely through your clothing, it gets trapped in your clothing, condenses and freezes.
 
            Famous arctic explorer Fridtjof Nansen made this observation in 1989: “During the course of the day the damp exhalations of the body had little by little condensed in our outer garments, which were now a mass of ice and transformed into complete suits of ice armor.” Nansen and his men were wearing nonporous outer garments of animal skins.
 
Homeostasis
Homeostasis is the medical term for the processes that control the equilibrium of your body’s temperature. To function properly, your body must maintain an even temperature around the vital organs (brain, heart, lungs, kidneys). A few degrees too high or too low can cause serious illness and death, if unchecked.
 
            The homeostatic process functions as your body’s thermostat, using your arms and legs to radiate heat away from your torso (head, chest, abdomen), similar to the cooling vents in a car’s radiator. When your body is producing excess heat maintaining a core temperature of 98.6 °F, the homeostatic process dilates the blood vessels in your arms, legs, hands, and feet. This allows full blood flow to the skin surfaces of your extremities.
 
            When working in a cold environment which threatens your body temperature equilibrium, the homeostatic process constricts the blood vessels, decreasing blood flow to your extremities as much as 99%. This is why your hands and feet get numb when you’re cold, and it’s why they are particularly vulnerable to frostbite.
 
            Because your brain needs oxygen to function, your body can’t cut off the blood flow to your head in order to conserve heat. Consequently, much of your body heat can be lost if your head and neck are not covered. Wearing a hat can even help keep your hands and feet warm. Because your hat reduces the loss of body heat through your head, your body can afford to send more body heat to your extremities. Knowing how heat is lost, you can minimize your bodies-heat loss, a priority in cold weather activities/operations.
 
 
Part I: The Human Body and Cold Weather
 
The best way to manage the cold is to gain a lot of weight, grow significant amounts of body hair, reduce your body temperature, and hibernate underground. Some animals, such as bears, have no problem doing this. Humans, on the other hand, are cruelly ill equipped to deal with harsh, cold temperatures.  
 
            When we get cold, an area of the brain called the hypothalamus—a gland that acts as our body’s thermostat—kicks into gear. Our teeth begin to chatter, our bodies begin to shiver, blood moves away from the surface of our skin, and the hairs on our bodies stand up. This is our body’s attempt to retain heat.
 
            At first glance, our thermoregulation system does not seem well designed. The hypothalamus is concerned mostly with keeping our internal organs warm. When faced with a choice between keeping the organs like the heart, liver, and brain warm, or keeping the extremities warm, the brain will definitely sacrifice more non-essential areas such as the legs, arms, feet, hands, and skin. The hypothalamus knows that you can live without a few fingers or toes—or even an entire limb—but you can’t live without your organs.
 
            Here’s how it works: When the hypothalamus receives a signal that indicates the body is becoming cold and needs to retain heat, it constricts the blood vessels in all “expendable” areas, limiting the amount of fresh, warm blood that can reach the extremities. This is called “vasoconstriction.” The less warm blood that reaches the extremities, the less heat is lost. The less heat that is lost, the warmer the internal organs remain.
 
            Areas that don’t receive a lot of blood flow to begin with, like fingers, toes, ears, and nose, can be significantly affected. Depending on the temperature and how hard the body is working at retaining heat, constriction can become so severe that almost no blood circulation exists in these areas. Feet and hands become extremely cold—painfully so—and in severe cases have little or no flexibility or agility. It becomes difficult to move them as designed, and simple tasks such as opening and closing fingers become impossible. As optimal function of both fine and gross motor skills are key to safety and success for both U.S. Military and law enforcement personnel, it’s necessary to reduce or minimize this issue.
 
            Because the skin can’t survive without at least some blood supply, blood vessels will dole out a minimal amount of blood to the extremities at key times. However, if cold exposure continues and becomes severe, and if the core temperature continues to drop, this function will eventually discontinue.
 
Increasing Activity
You can produce enough heat to maintain body temperature through exercise, even in very cold temperatures. Moving your body allows you to produce heat and make up for the heat that is being lost—at least for a little while. However, it’s not possible to sustain the amount of exercise needed to retain heat during long cold exposure, and eventually you’ll begin to lose heat faster than you are producing it. At this point your body will take over. You will begin to shiver, and your teeth will chatter.
 
Shivering     
This type of involuntary muscle action can increase heat production by up to five times. Unfortunately, like any “exercise” shivering requires fuel to keep it up. Being well-fed with high-energy food will help maintain your body’s ability to shiver for a longer period of time. However, there is a drawback to shivering. Because shivering is muscle activity, it will increase blood flow to the muscles, diverting it away from the internal organs. Shivering is a good way to heat up your body in the short term, but does not maintain core heat in longer exposures. While shivering may increase the feeling of warmth in the extremities, in fact it’s actually increasing heat loss.
 
Behavioral Responses
Another way to regulate core heat and avoid cold-related injury is to add layers of clothing. Insulating, warm layers of clothing will help maintain core temperature, and will also protect the skin from cold-related injury. However, adding insulating clothing or additional layers does not add heat. The body must produce heat for the apparel to preserve the heat. Do not wait until you are cold before adding additional layers of clothing. Adding layers BEFORE shivering occurs is the most efficient way to keep the body warm.
 
Frostbite
If the skin experiences long cold exposure without warming, the result is frostbite. If frostbite progresses beyond a certain level, there can be permanent consequences.
 
Frostbite occurs in stages, but these stages can progress fairly quickly. As we mentioned earlier, the hypothalamus will reduce the amount of blood flow to the extremities in order to keep the internal organs warm. Because skin can’t survive without some blood flow, it will open blood vessels periodically to send just enough blood to the skin. However, when prolonged cold exposure occurs, this system shuts down and the vessels no longer open. Without blood flow, the tissue becomes damaged.
 
First-degree frostbite, often referred to as “frostnip,” is identified by red, cold skin that may eventually feel prickly or numb. If the skin is warmed at this stage there is typically no long-term damage, though pain and tingling may be felt as the skin warms up.
 
If red skin turns white or very pale, the condition has progressed to second-stage, or “superficial,” frostbite. The skin often feels warm to the touch. Skin that is thawed at this stage will sting, burn, and swell, and may turn a variety of colors such as purple, blue, or mottled. In some cases, blisters filled with fluid may appear on the skin 24 to 36 hours after the skin has been warmed.
 
Severe frostbite is characterized complete numbness of the skin, which means you won’t feel cold, pain, or tingling. This level of frostbite extends through all layers of the skin—the epidermis and the dermis—as well as the subcutaneous tissue below all of the layers of the skin. In many cases of severe frostbite, the joints and muscles below the affected skin stop working. Large, fluid-filled blisters form 24 to 48 hours after the skin is thawed. Skin that has experienced severe frostbite where tissue has died will turn black and hard. Sometimes amputations are necessary.
 
Hypothermia
When extreme and sustained cold results in your body losing heat faster than you can produce it, the result is hypothermia. If not treated quickly, hypothermia can be fatal. Generally speaking, body temperatures that are 95˚ F or less are emergencies, and should be treated immediately. When body temperatures plummet to 95˚ F or below, irregular heartbeat can result in heart attack, and death.
 
            There are three stages of hypothermia, each of which is more severe than the stage before. It’s important to recognize and treat the early stages of hypothermia, as some of the symptoms in the later stages—for example, cognitive complications such as confusion and inability to make good decisions—result in hypothermia progressing without intervention.
 
Stage One: The most mild stage of hypothermia is characterized by shivering, confusion, and inability to think straight.
 
Stage Two: Moderate hypothermia is characterized by increased shivering, or shivering violently with sudden stops. Victims may be confused, unable to think, and groggy, and may slur their words. The pulse is typically slow and weak, and breathing is shallow, slow, and sometimes irregular.
 
Stage Three: When a person has reached the level of severe hypothermia he or she will stop shivering and lose consciousness. Breathing is infrequent and irregular, or there is no breathing at all. It’s not uncommon for people in this condition to simply “go to sleep” and die.
 
Challenge of Cold Weather
People are much more adept at functioning in temperate climates. The environmental situation—how cold it is, whether it is wet or windy—will determine how long it takes a person to become uncomfortably cold, and will contribute toward determining when frostbite, hypothermia, and other cold-related issues to set in. Additional factors that will determine the body’s response to cold include clothing, shelter, availability of food and water, activity level, body type, and gender. While the elderly and very young are susceptible to cold-related injury, the majority of cold-related problems occur to those who are outdoors, but who do not have adequate clothing.
 
Temperature
A person’s ability to handle a certain temperature is dependent upon the duration of cold exposure, as well as the ability to prevent or minimize heat loss through shelter and clothing. The physiological responses we discussed earlier in this manual, such as shivering and reducing blood flow to the extremities, will typically kick as soon as the hypothalamus detects heat loss. Because of these responses, the average, well-fed person can retain their core temperature in dry, still air, wearing only light clothing, in temperatures that are just above freezing. When temperatures drop, and when other environmental factors such as wind and moisture are introduced, more clothing must be put on to retain core temperature.
 
Humidity/Moisture
When objects come into contact with each other there is a molecular transference of heat energy called “conduction.” For example, if you sit on a cold rock or a steel chair, the heat from your body will be transferred to the other object. Conduction can also occur if your body comes into contact with water.
When you’re wet your body will lose heat up to 25 times faster than it would in the same temperature if you were dry. That’s because water is much more dense than air, and has a much greater heat capacity. The more humidity and moisture your body comes into contact with, the faster it will lose heat. For example, cold, wet air will cause your body to lose heat faster than cold, dry air, while being submerged in water will cause your body to lose heat faster than in any other situation. Boaters who are tossed into cold waters of 32.5˚ F or below have an expected survival period of between 15 - 45 minutes. People who are wet due to snow, rain, or perspiration at the same temperature have a much longer expected survival rate depending upon a variety of environmental and behavioral factors, but will still lose heat faster than those in the same temperature who remain dry. Staying dry is key to staying comfortable, performing your best, and reducing cold-related injury.
 
Wind
When one object is in motion—for example, if wind or water molecules move across the skin—the human body loses heat due to a process called “convection.” In the summer, during hot weather, we purposefully move the air by using fans to create convection, so we remain cool and comfortable. In the cold weather, moving air contributes to “wind chill,” a term used to describe the rate of heat loss in the body resulting from the strength of the airflow. The faster the air is moving, the faster we lose heat through convection. The human body can retain heat in freezing temperatures for significantly longer if the air is still; the windier it is—the more the air is moving—the faster heat loss will occur.
Convection can also result from the body coming into contact with moving water.
 
Perspiration
Regardless of the outside temperature, if your hypothalamus gets the message that your body is overheating it will increase blood flow to the skin in order to activate the sweat glands. When this happens, your body will lose heat during a process called evaporation, in which water (your sweat) is converted from a liquid to a gas as it is evaporated off your skin.
 
But sweating in cold weather is never optimal, even if it temporarily cools you down. First of all, excessive sweating is uncomfortable. Second, sweating can cause fluid loss and dehydration, both of which impair your ability to perform your best. Third, sweating can wet your clothing dramatically reducing its ability to keep you warm. Finally, as the weather cools further, or as wind picks up, the moisture on your body as a result of sweating cause an even faster heat loss.
 
Body Type
Are some body types more suited to cold weather than others? The quick answer is “yes.” While all humans are better suited to warm weather, some handle the cold significantly better than others.
 
Adaptation plays a large part in body type. In general, those who live in cold climates tend to develop the types of bodies that can handle the climate. That’s why you’ll see cold-weather natives walking around in their shirtsleeves outside, while visitors and tourists are bundled up in layers of clothing.
 
People with adequate, even body fat tend to handle the cold better than people who are too lean or too fat. Those who are too lean don’t have the fat necessary to retain heat, while those with too much body fat tend to have cold extremities because their skin is insulated from their body heat. Those who live in extremely cold weather climates, such as the Inuit, tend to develop an even layer of adequate body fat, which insulates the skin tissue, allows heat to be retained, and protects the core organs.
 
You don’t have to be a native to develop a cold-climate body. Regardless of your race, a fairly short exposure should acclimatize your body to the environment and make it better able to deal. On average, it takes about two weeks for a body to get used to a new environment; as a general rule of thumb it’s easier to adapt to a warm climate than it is to adapt to a cold climate.
 
There are other factors that will influence cold tolerance, specifically metabolism—the rate at which the body’s cells turn food into energy. People with high metabolisms tend to produce more heat than those with lower metabolisms. That’s why one person can be toasty warm in a room of 70˚ F, while another person will need to put on a sweater to be comfortable.
 
In addition, people who are active tend to experience warmer extremities in cold weather than those who don’t, as exercise promotes blood flow to the skin, hands, and feet.
 
Gender
Women typically experience cold hands and feet faster than men, which can make them more uncomfortable faster, but when the going gets tough women handle a cold climate better. Women conserve heat better than men, because they have more evenly distributed layer of subcutaneous fat. This layer of fat allows heat to be better stored in the core. So women are able to protect their core temperature better than men, but they also “feel cold” much faster because less warm blood is reaching their skin. While it may be easier for them to ward off hypothermia, because of their superior ability to retain heat in their core, women are more susceptible to cold-related injuries like frostbite.
 
Part II: How Technical Apparel Works
 
As we learned earlier, our bodies are constantly regulating themselves through the thermoregulation process to maintain a temp of 98.6 degrees. Our ability to maintain our core temperature and stay warm in cold weather will dependent on our environment—the temperature, and whether there are challenges to contend with such as wind or water that speed the body’s heat loss. However, to some degree we can help our bodies stay warm and comfortable during cold weather with our behavioral responses—in particular, wearing the appropriate clothing for a specific environment. In order to choose the right clothing, we must know how technical apparel works. This section of this guide is designed to give you the background you need to better understand the goals of technical apparel, and what you need your technical apparel to do in cold weather. A bit later in this guide, we’ll discuss the pros and cons of different types of technical apparel, and will show you how to put apparel together for maximum comfort and performance, depending upon the type of environment you are working in.
 
Layering
The key to staying warm and comfortable in cold weather is in layering. While it may initially seem counterintuitive, wearing several thinner layers is more effective at maintaining core temperature than wearing one heavier layer. Why?
There are a couple of reasons. First of all, depending upon the environment you need your apparel to breathe, insulate against the cold, resist wind, and repel water. You may need your apparel to do some of these things, or you may need it to do all. It’s not possible for one garment to do all of these jobs; you’ll need several to do the trick. In addition, if you’re outside for an extended period of time, there’s a good chance your environment will change to some degree or another. The temperature may become colder or hotter. It may rain, or stop raining. The wind could pick up. You may also exert yourself at various levels. All of these things will factor into the rate at which your body loses heat, and what kind of apparel you need to retain core body heat. You’ll want to be prepared to stay warm and comfortable in the worst conditions possible, but you’ll also want to be able to shed layers when you start feeling too warm. If exertion and environmental factors contribute to being too warm, you’ll begin to perspire. As circumstances change—if it becomes colder, windy, or wet, or if you stop moving—wet perspiration (and wet clothing) will cause your body to more rapidly lose heat, and you’ll become colder faster.
 
In addition, layering traps warm, dry air in between layers. This trapped air acts as insulation, reducing heat loss and minimizing discomfort.
 
Cold Hands and Feet
When the extremities become cold, common sense tells us to wear warmer mittens or boots, or to throw some chemical warmers into those items. But now you know that cold hands and feet mean that blood is being diverted away from the skin because core body temperature is dropping. While good boots and mittens are important for anyone who works or lives in a cold weather climate, if your core body temperature drops they really won’t help. When all is said and done, the best way to warm up your hands and feet is to add layers that breathe, insulate, and resist water and wind. You may need technical apparel with all of these components, or you may just need a couple of these features, depending upon your environment.
 
The Three Basic Layers
There are three jobs that must be done by your layers:
  • The layer closest to your skin must wick sweat and moisture away from the body.
  • The middle layer must insulate against the cold.
  • The outer layer must protect against elements such as wind and water, and in some situations sand and abrasion.
 
Layer 1: Wicking
If you’re exerting yourself in cold weather, or if environmental factors contribute to excess body heat, your body’s thermoregulation system will kick in and you will perspire. As mentioned earlier the body’s thermoregulation system is fairly sensitive, so it won’t take much for the sweat glands to open. A slick layer of sweat on the skin can result in rapid heat loss when the temperature drops, when environmental factors change, or when exertion drops off.
 
Breathable apparel will ensure that sweat does not get trapped next to the skin where it can result in moisture or dampness that will accelerate cold discomfort. A good, breathable fabric will have “wicking” power, which means the fibers will be constructed in a way that allows moisture to move away from your skin and through the fabric. The heat and humidity differential between your skin and the outside air works to push moisture from the hot humid environment near your skin to the cold, dry environment of the outside air. Wickable fabrics provide a path - basically the water molecules travel along the fibers. This is called capillary action. As the perspiration passes through the fabric, it dissipates and evaporates. The result is that your body stays warm, dry, and comfortable. When layering it is absolutely essential that the layer next to your skin be breathable and have wicking properties, but it is also important that protective and insulating layers are breathable as well. Dampness between any layer can cause you to feel clammy, cold, and uncomfortable.
 
Layer 2: Insulation
The insulation layer is designed to help retain core temperature by trapping heat close to the body. This is typically the heaviest and thickest of the layers, though current state-of-the-art fabrics and technology mean that “warm” is no longer synonymous with “bulky.” The key here is to maintain dead air space within the garment. These pockets of stable air provide excellent insulation against the cold. In addition, today’s insulating fabrics are very breathable, and most are designed to dry quickly. The best insulating layers use technologies that allow wetness and moisture to be moved away from the skin dispersed among their fibers while maintaining insulating properties even when wet.
 
Layer 3: Protection
The protection layer should guard against weather issues such as wind and water, and depending upon the situation may also be resistant to heat, fire, sun, or abrasion. Depending upon the environment you are living and working in, the protection layer may include some insulation, or it may simply be a shell. Most protection layers comprise tightly woven fabrics and state-of-the-art wind- or water-resistant coating or laminates that keep the elements out, but also allows perspiration and moisture to escape.
 
Part III: Fabric, Construction, and Design
In order for each layer to do its job, it must incorporate certain fabrics, construction, and design. In this section we’ll discuss the types of fabrics used for each layer and how they work, popular construction and design features, and how to care for different types of technical apparel. A little later in this manual, we’ll discuss what types of fabrics and technologies are most appropriate for specific weather challenges.
 
The Wicking Layer
The main job of this layer (also called “base” layer), which is worn closest to the skin, is to effectively regulate body temperature by providing warmth while also moving moisture away from your skin. This layer may also be used for sun protection, fire protection, and injury protection. For cold-weather conditions, the inner layer is typically available in a variety of weights, depending upon the climate, temperature, and activity level.
 
Wicking Layer Fabrics
Technology has led us a long way from the wet, clammy, cotton thermals Cotton is a natural fabric that retains perspiration and other moisture, takes a long time to dry (especially in cold conditions), is heavy when wet, and can leave its wearer vulnerable to discomfort and cold-related injury.
 
Another natural fabric that has historically been used as a base layer is silk. Silk is very lightweight yet extremely warm, is comfortable, and has fairly good wicking capability. Silk is an expensive fiber so most silk base layer fabrics are very lightweight and can be too fragile and require special care in laundering.
Polypropylene is one of the first synthetic fibers to be used as a base layer because it has excellent wicking properties. Unfortunately, polypropylene has a very low melting point so it can melt and cause injury if flame is present. It has to be dried at a very low temperature, or line dried. In addition, polypropylene can retain odors that are somewhat difficult to get rid of.
 
When it comes to base layer fabrics, the best choices are polyester fabrics or wool.
 
Polyester and microfiber polyester fabrics are superb choices for base layer, as they don’t absorb moisture, but do an excellent job of transporting it, spreading it out among fibers, and allowing it to dry faster.
 
The current generations of polyester, such as Capilene®, PowerDry®, and CoolMax® polyester, are materials that are commonly used in base layer. These polyester materials do an excellent job of wicking moisture and sweat, because the fiber is shaped to transport moisture or they are treated with “hydrophilic” surface finishes that allow them to improve their wicking capabilities. CoolMax® is a fiber that has channels to transport moisture. Some fabrics combine a microfiber polyester with a spun polyester and the difference in the size of the fiber causes the moisture to move from one side of the fabric to the other. Other alternatives include HydroSkin®, a synthetic fabric designed to reflect body heat back to you while minimizing water absorption, and CarbonTech®, a synthetic fabric made with activated carbon from coconut shells that claims excellent moisture management as well as UV protection and odor control.
 
Merino Wool. While many equate wool with the itchy, rough sweater knitted by grandma, fine gauge wool (17 – 19 denier) that has been properly processed for technical apparel is soft, comfortable, warm, lightweight, does an excellent job of wicking moisture away from the body, and naturally resists odors. Wool also continues to insulate when it is wet, and has a fairly good warmth-to-weight ratio. Wool has a natural UV protection, is fire retardant, and won’t melt or stick to the skin if exposed to high heat. If even the finest wool feels itchy, blends with wool and synthetics are a good option.
 
Wicking Layer Fit
Base layer should be thin, light, and body-hugging. It should also have maximum stretch (either in the weave or the fiber), to allow for comfort and freedom of movement. Garments that use Spandex or Lycra® for stretch can lengthen the drying time of the Wicking Layer. Stretch garments as a base layer become dense and are so close to the body that they are very slow to dry.
 
Caring for Your Wicking Layer
Polypropylene fabrics require extra care when laundering, as they will shrink if exposed to high heat. Polypropylene base layer should be washed in warm or cool water, and either air-dried or machine dried on a lower heat setting. Because these fabrics tend to retain odors, being unable to wash in hot water may make it difficult to get this fabric truly clean and fresh. Polypropylene has a tendency to “pill” after extended wear or after several washings, but turning the item inside out before washing may prevent or reduce this tendency.
 
Polyester fabrics can typically be washed in any temperature, including hot, with ordinary laundry detergent and bleach. Stains and odors can usually be successfully pre-treated. Polyester materials should be dried in a dryer at a medium to low temperature setting. Fabric softeners are not needed on polyester base layer garments and will inhibit performance over time.
 
Wool can be machine washed in lukewarm water on the gentle cycle, with mild detergent without bleach. Wool base layer can also be machine dried at medium to low temperature, though it should be turned inside out to prevent pilling. Avoiding high heat in the washer and dryer will prevent shrinking.
 
The Insulating Layer
The job of this layer, which is worn between the inner and outer layers, is to help preserve core body temperature by keeping heat in and cold out. This is done by trapping air between insulating fibers, as well as by effectively wicking away moisture. Depending upon the environment, some insulating layers may also include water and wind repelling technologies.
 
Insulating Layer Fabrics
There are a variety of natural and synthetic fabrics that make an excellent insulating layer.
 
Natural fabrics. Wool and down feathers are two of the most commonly used natural fibers in insulating layers.
 
Wool is extremely warm, has a good warmth-to-weight ratio, and naturally wicks away moisture. In addition, wool retains its insulating properties when wet. As discussed in the previous section, today’s technologies mean that wool is no longer thick, scratchy, or uncomfortable. Mid-to heavyweight-insulating layers can be soft and comfortable. The downside to wool is that insulating layers can be slightly heavier than other materials. Wool fiber is absorbent, that’s what makes it comfortable to wear, but it does get wet. Its unique property is that it will still provide insulation when wet.
 
Goose Down is another natural material frequently used in insulating layers. Down is one of the best insulators available as the soft fibers are outstanding at trapping dead air. In addition, it has the highest warmth-to-weight ratio of any fiber and is highly compressible, making it easy to pack and carry. The drawbacks to down are that its loft makes the garment puffy and thick, no longer insulates once it becomes wet, and dries very slowly. Also, as garments age the down can clump, if not properly cared for, which can cause both hot spots and cold spots in some areas.
 
Down needs to be held in place in a garment. This is commonly done through quilting. Quilting is the process of sewing seams through a garment (or a sleeping bag) to create pockets that hold the down in place. While this stabilizes the down, it also creates cold spots along the seam where the down is compressed or non-existent. Expedition down garments will have baffles that create chambers for the down. This eliminates seams going through the garment that result in cold spots. Most down apparel on the market has stitch through construction.
 
Down comes in various weights – called fill weight. 600 fill down is pretty good. 800 fill down is outstanding and will have the highest warmth-to-weight ratio.
 
Synthetic fabrics. Polar fleece such as Polartec® is one of the most often used fabrics in insulating layers, and with good reason. Fleece, which is a polyester pile material, is warm, breathable, and insulates when wet. It’s lighter than wool, and its construction creates good dead air space, helping to maintain core body temperature. In addition, fleece allows perspiration to evaporate through its fibers because polyester will not absorb moisture. Fleece is soft, incredibly comfortable, and comes in a variety of weights that can be selected based upon the environment and activity level of the wearer.
 
Fleece’s main drawback is that it’s highly flammable unless treated, and is fairly wind-permeable. Several manufacturers have solved the wind issue by developing “hard” fleece, such as some of the (you may want to refer to Soft Shell fabrics ) Tweave fabrics as well as Polartec’s Power Stretch® and Wind Pro®, that comprise a nylon or polyester, water- and wind-resistant outer shell on the outside and traditional fleece on the inside. These withstand the elements, but also maintain fleece’s trademark breathability and comfort. Other hard fleeces, such as Polartec® Windbloc® and Gore WindStopper®, have a hidden membrane designed to repel wind.
 
Other synthetic insulating layers are comprised of quilted polyester material or fill, such as PrimaLoft®, Climashield® or Thinsulate®, that is lightweight, compressible, breathable, and provide excellent insulation. While these synthetic fibers don’t have as great a warmth-to-weight ratio as natural down, they insulate when wet, dry quickly, and absorb little moisture. Most of these technologies provide excellent warmth for the amount of thickness used. When paired with a wind-resistant and water repellent fabric on the outside, the synthetic insulated garments can provide some additional protection from the elements.
 
Insulating Layer Fit
Fit of the insulating layer is crucial. It should fit close to the body, to allow for trapped air, but not tight. A tight fit may compress the insulation decreasing its ability to trap dead air and retain heat. A very loose fit will force the body to generate a lot of heat to warm up the dead air created by all the extra space inside the jacket. Then, if the wearer moves, this heat will be pushed out and cold air will move in and have to be heated up again.
 
Caring for Your Insulating Layer
Of the natural fibers, wool is the easiest to care for, and can be machine-washed and dried on the gentle cycle using a mild laundry detergent without bleach. Because wool is naturally resistant to odors and stains, it is easy to clean and can withstand many washings. To prevent pilling of wool, garments should be turned inside out before washing and drying.
 
Down is less durable and requires more care. While most down-filled apparel can certainly be laundered at home in warm or cool water using gentle detergent, repeated washings eventually cause down to lose its insulating “loft.” In addition, air-drying down will cause it to smell, but any heated drying at all can burn feathers, or cause them to clump. Down insulating layers should be dried in the dryer on the “air” setting only. To minimize clumping, a tennis ball or two should be thrown into the dryer with the apparel.
 
Synthetic fabrics are typically easy to care for. Fleece can be thrown in both the washer and the dryer on warm settings, with no risk to its insulating properties. To prevent pilling of fleece, wash and dry it inside out. Also, be sure to read the care instructions on “hard” fleece and insulated garments, as protective treatments or coatings may contraindicate the use of fabric softeners or bleaches. Insulating layers that use synthetic fill can typically be washed or dried on warm settings as often as possible, with normal laundry detergent, and are very durable. Synthetic materials should not be dried in a hot drier or they could be damaged.

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