Before introducing the types, let’s do a short intro on how heat transfers (no mathematical relationships here, just basic concepts ^^). Heat is basically thermal energy and there are 3 ways it can transfer, conduction, convection and radiation.
To illustrate the 3 processes, let’s use the example of a boiling kettle. Conduction is a contact process, so conduction occurs only if 2 bodies are in contact with each other, i.e. touching the kettle causes heat to flow from the boiling water to the finger by contact, scalding the finger. On the other hand, convection transfers heat through fluid flow, i.e. placing a palm in the path of steam leaving the kettle causes heat to flow from the boiling water to hand via the convection of steam, scalding the palm. Radiation is a process which requires no medium for heat transfer; heat is transferred in the form of electromagnetic radiation (of which visible light is one component), i.e. despite standing a distant from the kettle stove, heat is still felt because heat is being transferred via radiation from the flames to the body, another example is the heating of the Earth which is due to solar radiation through the vacuum of space.
With the concepts behind us, let’s discuss the clothing system. 3 layers are used when dressing cold and most materials will refer to them as the baselayer, the midlayer and the outershell. These 3 layers do not create heat to keep warm; rather they are used to reduce the speed which heat is loss from the body.
Baselayer
The purpose of the baselayer is to reduce heat transfer via conduction. It does so by keeping the skin as dry as possible because when the skin is wet, heat flows from the skin to the layer of moisture on the skin. The baselayer might also be known as long john however unlike the common long john which is made of cotton, aerobic activities in the cold prefer the use of baselayers made of either synthetic materials or wool. Wool and synthetic materials are preferred over cotton because cotton takes a much longer time to dry and with the amount of sweat which can be produced during aerobic activities, wearing cotton is a recipe for hypothermia. Between synthetic and wool, the choice is up to the individual. Main differences between each are, wool is usually more expensive than synthetic, wool usually takes longer to dry, wool doesn’t stink as badly compared to synthetic after many days of wear, for the same weight wool is warmer than synthetic, wool is warmer than synthetic when wet (debatable).
Midlayer
The purpose of the midlayer is to reduce the heat transfer via conduction (depending on the type of material used, heat transfer via convection is also reduced). Air is an excellent heat insulator (non debatable fact) which the midlayer utilises. The midlayer functions by trapping a layer of air around the body, creating a temperature buffer which prevents heat transfer to the surroundings. To trap air, 2 types of midlayers can be used, down or fleece. Fleece looks like a fuzzy jacket and is made of synthetic material. The fuzzy, fibrous portion traps pockets of air in the jacket, forming the insulating layer of air around the body. Down can be either synthetic down or natural down (goose down, duck down etc). Like wool vs synthetic, there are camps for synthetic and natural down. Main differences are, natural down is harder to dry compared to synthetic, natural down is warmer for the same weight compared to synthetic and natural down is more compressible compared to synthetic. Synthetic is recommended over natural for mountains which experience a lot of wet snowfall or rain. If the midlayer is also windproof, the midlayer also prevents heat transfer via convection since wind blowing against the body will not be able to penetrate the midlayer and draw heat from the body.
Outershell
The purpose of the outershell is to protect the body from the elements of wind and precipitation and is at least water resistant. The outershell reduces heat loss via convection and radiation. Outershells are windproof which prevents heat loss via radiation using light colored inner layers to reflect radiation emitted back to the body. The lists of materials that can be used to make waterproof outershells, also known as hardshells are numerous of which the most famous are eVent and Gore-Tex. It is not recommended to use nylon, ponchos and their derivatives as hardshells although they are still waterproof. This is because nylon and co are waterproof but not breathable and not being breathable means sweat from aerobic activities will be trapped within the hardshell, eventually soaking the baselayer and midlayer underneath. Although there are sceptics because waterproof/breathable membranes sound like something from sci-fi, it has been proven that this materials do work but only if taken care of.
Current advancements are attempting to combine the outershell and the midlayer, forming a new class known as softshells. Softshells address the breathability problems that frequently plague hardshells. However this achieved by trading the waterproof protection for a water resistant protection. Hence, softshells see excellent use in conditions where precipitation is little and dry and it is mostly windy. Technological advancements are constantly pushing the boundaries so hardshells might disappear altogether some day. Only the future can tell.
Captured above are the general strategies to clothing in the cold. This applies not only to the body but also to the head and hands. Most people skip using baselayers/liners for the head and hands though and go straight to the midlayer fleece which works just as well. However, there is an exception with regards to the feet.
Most boots in mountaineering are not sufficiently breathable despite their waterproof/breathable claim. As a result, sweat from the feet which stays in the boot freezes overnight which leads to uncomfortable morning starts and risk of hypothermia. Double boots attempt to alleviate the problem through the use of a removable inner liner which can be removed and dried in the sleeping bag during the night. However, not many adore the weight of such double boots, preferring the lightness of single boots and their increased mobility. Besides using different types of boots to work around the problem of freezing sweat, another method is to use socks which create a vapour barrier between the feet and the boot, i.e. prevent sweat from reaching the inner surfaces of the boot. To do so, liner socks are worn as the first layer with wool socks forming the second. Liner socks move sweat away from the skin while wool socks absorb any excess moisture which cannot be evaporated, keeping the boot and skin dry. Going to extremes, another layer, waterproof socks can be added over the wool to ensure no moisture reaches the inner surface of the boot at all.
Yup yup, guess that’s about all there is to know. There are many other exotic systems like the buffalo system or waterproof materials like paramo. Google will be your best friend for this.
