 A basic layering system has three important functions, to wick sweat away from the skin, to trap body heat and to protect you from the weather. Each part of your clothing serves a different purpose and works with the other layers to keep your skin dry, warm and comfortable. An effective layering system allows you to adjust and regulate your body temperature when active, resting or as the weather conditions change. The first layer, which is worn next to the skin, is known as a base layer. A base layer's main function is to wick sweat away from your skin and towards the outer fabrics, helping you to regulate your body temperature. Moisture conducts heat 25 times faster than air, so if it can't escape the surface of your skin, you'll become cold very quickly. Quality base layers are generally made from polyester or merino wool. Cotton should be avoided at all costs, as this material soaks up moisture and holds onto it, which means that you quickly become damp, clammy and ultimately cold. The second layer, known as a mid-layer, is any piece of clothing worn over your base layer and or under your outer layer. The main purpose of this layer is to keep you warm by trapping body heat while continuing to allow moisture to make its way to the outer layers. Mid-layer choices can vary greatly, but the microfleece hood is all the way to down-filled vests and which you choose depends on conditions and activity. The microfleece garments are very practical, quick drying and make a great option for high outback activities. Mid-to-heavy weight fleece jackets are more suited for colder conditions, they can weigh more than other forms of insulation and aren't as compressible. Synthetic insulators are a versatile and practical option for a lot of people. Strands of synthetic fibre create a down-like material that traps heat effectively. It continues to work when wet, dries quickly and is generally quite easy to care for. Weightful weight down is the best insulator available, with the exception of expensive hydrophobic down it must be kept dry to be effective. This means it's best saved for cold but dry days. Your outermost layer is the main defensive barrier against wind, snow and rain. By preventing further moisture from getting into your clothing it allows base and mid-layers to continue to wick moisture away from the skin. For a layering system to work well your outermost layer must be both waterproof and breathable, stopping snow and rain from entering but allowing sweat vapour to escape. There are many different ways of constructing an outer layer but most are formed of a stiff outer face fabric for durability followed by a waterproof, breathable membrane such as Gore-Tex. It's important to remember that a layering system should always be versatile, you should be able to strip a layer off to cool yourself down or add a heavier weight layer to increase warmth.