Gear
Layering
Three layers, one job each. The failure mode is almost always moisture you produced yourself.
Layering is described everywhere and understood less often. Each layer has one job, and the system fails at the point where moisture from your own body gets trapped rather than moved.
Base: move moisture
The base layer's job is to shift sweat off the skin, not to insulate. Merino wool resists odour, insulates reasonably when damp and dries slowly; it is also less durable. Synthetics dry faster, last longer and smell. Both work. Cotton does not: it absorbs many times its weight in water, holds it against the skin, and cools you by evaporation exactly when you need the opposite. In cold wet conditions that is not a comfort problem, it is a hypothermia mechanism.
Mid: trap air
- Fleece breathes well, keeps working damp, and is bulky for its warmth.
- Down has the best warmth for weight and collapses to nearly nothing when wet, because the loft that does the insulating is gone. Excellent in a dry cold climate, a liability in an Atlantic one unless kept dry.
- Synthetic insulation retains most of its performance damp, weighs more and packs bigger. In western Norway this is usually the right compromise.
Shell: stop wind and water
Covered separately in rain shells. Wind resistance alone is worth more than people expect: moving air strips heat far faster than still cold air does.
The actual skill
Regulate before you sweat, not after. Strip a layer at the bottom of a climb while you are still slightly cold, rather than at the top when you are already wet. Being briefly uncomfortable at the start of an ascent is the whole technique, and it is the difference between arriving at a windy summit dry or soaked.