Similar to the ECWCS Gen III (Extended Cold Weather Clothing System) developed by the US Army DEVCOM for American soldiers on cold weather missions, French soldiers also have new technical clothing specially designed to withstand the harsh weather of moderate to extreme cold climates. Developed by the leading brands specializing in high-performance cold weather clothing, these technical garments come in 3 levels of protection that, when combined, form an optimal cold weather protection system.
Base layer / First layer
Belonging to the first two levels of protection of the American ECWCS (the US Army's cold weather clothing is classified into 7 levels comprising the ECWCS), the "base layer" or "first layer" garment, has the function of wicking away moisture and keeping the body dry. It is essentially the first insulator in direct contact with the skin. Usually made from polyester, polyamide, or polypropylene fibers and elastane, this primary layer is thin and stretchy and is worn very close to the body.
Depending on the manufacturer, you will have a choice between several types of base layers. The difference lies in the fabric composition; the thicker the fabric, the warmer it will be. In any case, the base layer remains a primary layer, a second skin if you will, and is worn in conjunction with a mid layer and outer layer garment for the coldest climates.
Mid layer / Intermediate layer
The "mid layer," also called the "second layer" or intermediate layer, is a garment worn depending on the intensity of the cold, with or without a base layer. It is not worn close to the body but in a fitted manner, adding an extra thermoregulatory protection for the user. It is a type of fleece jacket or softshell jacket, often zipped along its entire length or featuring pockets. Mainly made of polyester, the mid layer is both breathable, lightweight, and comfortable. Sometimes waterproof, it generally has windproof and water-repellent properties, thus providing good thermal protection for the soldier.
For extreme cold climates, there are also long mid layer pants that are much warmer than base layer pants. Mid layer pants act like tights or a second skin (unlike a mid layer jacket or t-shirt) and cannot be worn over base layer pants without significantly restricting your movement. However, they can be perfectly worn under cargo pants.
Outer layer / Third layer
The outer layer, or "third layer" in English, is a garment that is in direct contact with the elements. It is simply a jacket or parka specially designed for the cold. Often featuring a technical membrane such as Gore-Tex or Dintex, and a high-performance insulating filling such as G-Loft, this third layer is warm, comfortable, breathable, windproof, and waterproof.
Should you wear these 3 protective layers together?
Sometimes you will need to combine these 3 layers for optimal protection, sometimes only 2 or even 1 will suffice. It all depends on your mission.
The more layers you wear, the warmer you will be, but you will also lose ease of movement. Keep in mind that a moving body produces heat, so if you wear an outfit that is too warm from the start, you risk overheating and thus a decrease in your physical performance, which could jeopardize your mission. The best thing to do, as before any mission, is to gather as much information as possible about the type of terrain and climate you will encounter. Do not hesitate to talk to your colleagues or superiors who will surely be able to advise you well.