Being comfortable in any weather comes down to one thing - layering. When you layer your clothing you surround your body with a personal microclimate that can be adapted depending on moisture and wind conditions, temperature, and exertion. To get the most comfort out of your layers, choose brands and items that are made from high quality fabrics and fibers and are design to fit for the activities you’re using them for.
BASE LAYER The first layer you wear is the most critical (yes, this includes your undies) because it’s in direct contact with your skin. High performance base layers, also referred to as underwear, pull moisture away from the skin and allow it to disperse it to the air or outer layers where it can evaporate. This is important because damp garments draw precious heat away from your body. Even in conditions above freezing, rapid heat loss can cause a dangerous drop in your body's core temperature.
Most manufacturers offer base layers in light, medium, and heavy weights. Light layers suit aerobic activity where sweat dispersal is paramount. Midweight underwear provides moisture control and insulation for stop-and-go activities. Heavy layers are best in very cold conditions, or when you're relatively inactive.
MID-LAYER The main function for mid-layers is to provide insulation. This layer must also be able to continue the transportation of moisture from your base layer. Look for fabrics and fibers that work to slow heat loss and help to retain the warmth generated by your body. Both merino wool and synthetics are well suited to this because the structure of the fibres creates small air spaces that trap molecules of warm air.
Additional features can include secure phone and ipod pockets, thumb holes to keep sleee inplace, pit zippers and full-length front zippers to allow venting, and others.
OUTER LAYER Your top layer should protect you from the elements while allowing air to circulate and excess moisture to escape.For dry conditions, a breathable (uncoated) wind shell or a smooth-surfaced soft shell may be all you need. If you expect conditions to be more severe, a waterproof (coated) jacket might be adequate. A shell made of a breathable and waterproof fabric, such as Gore-Tex, will protect you from wind and rain, and allow water vapour to escape.
Insulated jackets and pants provide extra warmth in extreme conditions or allow you to forgo wearing a mid layer in some conditions.