Clothing might seem like an afterthought when one is headed outdoors or planning for an adventure. Still, it’s the first and most important layer of protection between you and the elements. No level of skill or planning can make up for ill-chosen clothing if the weather takes a turn for the worse. It’s essential to understand the fundamentals of layering to make sure you can stay safe in any conditions.

To understand the use of clothing, it is first essential to understand heat. In simple terms, heat is energy. The more energy there is in a system, the more heat there is in the system. Temperature is a measure of heat. There is no such thing as ‘cold.’ When something is cold, there is less energy or less heat.

Another important fact to know is that the human body is only about 10-25% efficient in processing the food that we eat into energy. All of the unused energy is given off as heat. That heat is always leaving our bodies. The normal human body temperature is averaged at around 37ᵒC (98.6ᵒF). Since the air around us is usually much cooler, heat is always leaving our bodies. All we can do is control the heat flow as it leaves our bodies. If the body can’t divest the excess heat, the human core temperature raised above the average temperature, and we become very hot. That is known as hyperthermia. If we give off heat too quickly, then the body temperature drops, and we become very cold. This is known as hypothermia. Clothing is designed to control how much, and how quickly, heat can leave the body.

Body Heat is Given off in Three Ways

Radiation

Radiation is how most heat leaves the body. Heat loss by radiation is continuously occurring during the winter months when temperatures fall significantly below this threshold.

Conduction

Conduction occurs when the body is in contact with any object that is cooler than the body. Heat loss by conduction can be a significant issue when in contact with snow, ice, or cold water.

Convection

Convection occurs when the heat is transferred away from the body through circulating air currents. This is like sitting in front of a fan, and it’s why we feel cooler when the wind is blowing. Heat loss by convection can be significant during winter storms with exposure to the wind.

Note: Evaporation is the process that occurs when you sweat. It utilizes all three methods of heat transfer and is not a separate method.

It is crucial to keep in mind the different ways that heat is lost from the body to understand clothing. Heat moves from hot temperatures to cool temperatures. No heat can be transferred when two objects are at the same temperature. When air temperatures rise, radiation no longer works, and the body relies on convection and conduction. Water (sweat) is poured onto the skin to facilitate heat loss by wind and conduction. When the air temperature becomes the same as the body temperature, then no heat can be lost from the body, and the body temperature will start to rise dramatically. Hypothermia occurs if a body loses heat too much and too fast.

When it is cold, we bundle up to keep heat in, and when it is hot, we take clothes off to allow more heat to leave our bodies. One of the most excellent conductors of heat is water. One of the poorest conductors of heat is air. For example, in the summer, when we want to conduct heat out of our bodies, we go swimming. If we want to keep heat in our bodies, we will surround ourselves with air. Fibres and fabrics, such as wool, are excellent insulators because they have a lot of air in them. Since water is a good conductor of heat, the inside layers of clothing are designed to move or ‘wick’, water away from the skin.

Layering

Heat transfer out of the body is best controlled with clothing worn in layers. Body heat is trapped in the dead air space in the middle layer creating insulation, while perspiration is wicked away from the skin and through to the outer layer to prevent conductive losses. Wind and rain cannot penetrate the outer layer, therefore limiting convective heat loss. Not all clothing is designed to insulate.

Base layer

This is the layer of clothing directly against your skin, and its purpose is to wick sweat away to keep you dry. This includes socks, underwear, and an initial pant/shirt base layer if in colder conditions.

Middle layer

The middle layer is for insulating. This layer functions to retain body heat by creating ‘dead air.’ This can be clothing such as shirts and pants, thus an extension of the wicking layer.

The Outer layer

The outer layer, or shell, is a water- or wind-resistant barrier between you and the elements, keeping the wind from blowing across someone and causing convection loss of heat. If you don’t plan on wearing these three layers throughout your trek, it would be prudent to at least pack these types of layers to have just in case. The benefit of the layering system is flexibility. If conditions change, you can always peel off layers to cool down or add layers if the weather takes a colder turn. However, if you don’t pack those essentials, you might be left out in the cold.

Some clothing will help move heat away from the body. For example, in hot environments, loose-fitting clothing should be worn to move heat away from the body, as this facilitates ventilation.

Types of Fabric

What types of fabric are more appropriate to wick water from the skin, insulate from heat, or even facilitate heat loss? This topic has been discussed by recreationists of all experience levels. It can take some experimentation to figure out what works best for you. Here are some basic guidelines to consider when choosing the fabric that best fits your activity and goals:

Wool

Wool is a very popular choice and with good reason. Wools 3D wavy crimp-type fibres trap air easily. Eighty percent of the material is air. It’s an excellent insulator and will keep body heat contained in cold weather. Wool also absorbs a lot of water. For example, merino wool is capable of holding 30% of its weight in water absorption before the wearer can even feel it on their skin. Even with the water that it has absorbed, the wool maintains insulation, which is a huge plus for this material. Wool is also wind resistant. These properties make it an ideal fabric choice for most activities. Many people use wool as their base layer. Once maligned for being itchy, ultra-fine merino wool is itch-free, naturally breathable, moisture-wicking, fairly fast-drying, and not prone to odours.

Polyester and Nylon

Polyester and Nylon are synthetics, such as fleece, that offer quick-drying capabilities at a more affordable cost. These fabrics are quite durable and make great slacks and shirts. Synthetic fibres have 3D patterns that imitate wool. Synthetics are warm when wet, but do not absorb moisture. They dry quickly, are as warm as wool, and are only half the weight of wool. One problem is that synthetics have poor wind resistance. They can also develop an odour worse than wool. Overall, however, synthetics are a fantastic and affordable option that many choose as their base layers.

Down

“Down” is the under plumage that is found beneath the feathers of ducks, geese, and other waterfowl. It is natural insulation. Goose-down insulation itself does not consist of feathers. Goose down frequently contains terms like “600+ fill goose down” or “900+ fill goose down” lines. These numbers indicate how much goose down is actually added to the coat or sleeping bag, for example. This is known as the “fill rating.” The higher the number, the more goose-down insulation is added into the coat or sleeping bag, and the warmer it should be.

Down is very soft, provides excellent insulation, and is very lightweight. It must be packed in compartments for this reason. It is excellent to use for sleeping bags and coats as it packs well, and it conforms to the user. The problem with down is that it will clump when it is wet and lose its ability to create dead air space, thus losing its insulative ability.

Silk

Silk is a soft, luxurious fabric that is quite thin and light, making it a great choice for moderate, cool weather conditions. The downside is that it doesn’t wick moisture away from the skin as well as wool or synthetics, so it isn’t a good option for warmer days or activities with a great deal of exertion. Another consideration of silk is that, like synthetics, it can be prone to odour. The softness of silk also results in it being a less durable fabric, and its vulnerability to abrasion and sunlight results in a shorter lifespan than the other fabrics discussed.

Cotton

Cotton is never a good choice for outdoor activities, even when layering. There’s a reason that experienced recreationists use the phrase “cotton kills.” Cotton does not effectively wick moisture away from your skin, it doesn’t dry quickly, and it is a very poor insulator. While wool will keep you warm when you’re wet, cotton will keep you cold when you’re wet. Even cotton socks should be avoided, as wet and cold feet are a recipe for disaster. So, in reality, cotton does not kill, but hypothermia does. It’s easier to get hypothermia when you wear cotton, not because it doesn't insulate you as well as other materials, but because it just doesn't insulate you as well when it is wet. Cotton is a comfortable and cheap option for lounging around at the campsite but should be avoided for active pursuits.

Synthetic Fibers

Synthetic fabrics are human-made and produced entirely from chemicals to create fabrics like polyester, rayon, acrylic, and many others. Natural materials, such as cotton, silk, and wool, are made of animal and plant-based fibres.

Over the years, synthetic fibres have increasingly grown in popularity. They are resistant to insects and fungi and have little to no ability to absorb moisture. Synthetics can easily create dead space. And because they are usually cheaper to produce, they are cheaper to buy.

A serious drawback of synthetic fibres is that they will melt. Since they have little to no ability to absorb water, they will always insulate, even when wet. This makes synthetic clothing ideal in wet environments like river trips. However, synthetic clothes are heavy and do not pack well, so they are not suggested for hiking.

Microchannels can be created in the fibres to create Quallofil and PolarGuard. Quallofil is made by Du Pont and is used both in sleeping bags and in many insulated jackets. The problem with Quallofil is that it is a bit on the heavy and bulky side. Polar guard, and all its various derivatives, is considered the “premiere” synthetic insulation and is used in most high-quality synthetic sleeping bags and clothing. New iterations have made the material significantly less bulky, while at the same time improving the insulating abilities by around 10%.

Super thin fibres are small synthetic fibres. They are very tiny, so manufacturers can put more of these in clothing. That means dead air space and more insulation. Since they are small, they are also light and pack well. They stay dry and keep their warmth when wet. There are not too many negatives with this material. Primaloft and Thinsulate are examples.

Tying it all Together

Now that you’ve learned about the basics of layering, fabric types, and sun protection, it’s time to bring it all together. We’ve discussed the three main layers (sweat-wicking, insulating, shell) and three optimal fabrics (wool, synthetic, silk), but how do you combine those?

The Base layer (wicking).

This layer needs to be one of the high-performance fabrics, such as wool, synthetic, or silk. Its purpose is to wick sweat away to keep you dry. Many consider this to be the most important layer of all, as this is the layer that keeps you cool and comfortable when you’re working up a sweat. The weight of this base layer can also change depending on the season and activity. Examples of wicking layers are Capilene, Lifa, and Dryline.

The Middle layer (insulating).

The middle layer functions to retain body heat. This is the layer that will keep you warm and is typically the thickest or heaviest-weight material of the three. Wool and down are popular choices for mid-layers, but you can also choose fleece or synthetics with high-loft options such as Polar-guard, Micro-loft, and Primaloft. For wet weather, it would be wise to choose those synthetic pile or fleece options, as down can get soggy and lose its insulating capabilities in very wet conditions. Synthetics are also breathable and easier to ventilate and wash. A good rule of thumb for the mid-layer in colder weather would be to plan on wearing a synthetic as your go-to and to always pack an extra down jacket. Down “puffies” is easily compressible and lightweight, so they add substantial function at a low weight.

The Outer layer (shell).

The outer layer is a water- or wind-resistant barrier between you and the elements. Being the first line of defence against the elements, this layer needs to be able to repel rain and snow while simultaneously being breathable. You don’t want your perspiration to build up inside your layers; that would defeat the purpose altogether. In very wet conditions, go for something completely waterproof, with features like sealed seams, zipper guards, and cinch-able hoods. Things like armpit zips and mesh pockets can help you ventilate even while working up a sweat in wet conditions. In drier conditions, you can consider using a lighter shell that is just windproof. These typically aren’t very waterproof but are highly breathable, and pack down small enough to fit into a pack.

Now that you know the essentials of dressing for the outdoors, you can simply mix and match your layers to prepare appropriately for any conditions. Remember that what you wear is what is keeping you safe against whatever mother nature throws at you. There is no bad weather, only bad clothing.