What it is, why it works and how to make it work for you
Layering is all about delivering flexibility and comfort; comfort being warm or cool as suits whilst also staying dry. For active outdoor pursuits both need a little explanation.
Wearing layers of clothing rather than one chunky jacket allows you to adjust how much you’re using quickly and easily. It means that by shedding a layer or two and opening zips for ventilation you can avoid overheating slogging up a steep hillside. When you reach the top, replacing the layers means you will not get chilled.
The layers – next to the skin or base layer, mid layer and outer layer - work together to deliver aspects of comfort other than just wrapping up warm. Modern synthetic fabrics are quite sophisticated in the way they work with your body – different weights in thermal garments offer warmth options whilst others are more suitable for highly aerobic activities where lots of body heat is being generated. Our bodies are always giving off moisture vapour just by breathing and expending energy always generates heat; we avoid overheating by sweating.
Base layers work in a layering system by not absorbing sweat nor allowing body moisture vapour to condense into liquid but instead let both through the fabric unhindered to then pass through the insulating mid and wind/waterproof outer layers to be dissipated in the atmosphere. Windproof/waterproof outer layers help to conserve body heat trapped in the layers underneath and, by being breathable, avoid condensation forming and soaking clothing.
The performance of modern layering systems and fabrics is probably best understood by wearing a cotton t-shirt under a non-breathable jacket and powering uphill. Before long, the t-shirt will be soaking wet and condensation will be running down the inside of the jacket. As the moisture evaporates, it will draw body heat away, chilling you and, of course, being potentially dangerous, especially in the mountain environment.
So, flexibility and the many faces of comfort are central to the purpose of a layering system. As the wearer, it’s up to you to manage body heat retention and loss to suit yourself, your activity, the weather and the outdoor environment. It’s not a static system but works interactively with all those factors.
Essential elements of any layering system are hats and gloves as they are the most flexible to shed or add and have an almost instant effect on cooling down or warming up.
Base Layer – warm or cooling options both allow moisture through rather than soaking the fabric, chilling the body and feeling very uncomfortable; both options aim to avoid the feeling of clammy skin.
Mid Layer – essentially offering insulation by trapping air warmed by body heat but not absorbing moisture and becoming wet. Natural or synthetic materials and fills are available in a variety of styles and warmth values.
Outer Layer – protecting the underlying layers from wind, rain and snow, breathable fabrics ensure moisture can be transferred to the atmosphere rather than accumulating on the inside.