Hypothermia is the silent killer. It doesn't strike suddenly; it creeps in as you sweat, rest, and cool down. The solution is not one giant coat, but a system of layers that can be adjusted to regulate body temperature.
1. Base Layer (Management)
Goal: Move moisture (sweat) away from skin.
Material: Merino wool or synthetic (polyester). NEVER Cotton. "Cotton kills" because it absorbs moisture and loses insulation value when wet.
2. Mid Layer (Insulation)
Goal: Traps body heat.
Material: Fleece, down, or synthetic loft. Down is warmer for its weight but useless when wet. Synthetic insulation retains warmth even when damp.
3. Shell Layer (Protection)
Goal: Block wind and rain.
Material: Gore-Tex or similar waterproof-breathable fabrics. It must vent moisture out while stopping wind from blowing heat away.
"Be Bold, Start Cold"
When starting a hike, you should feel chilly. If you start warm, you will be sweating in 10 minutes. Sweat in freezing temperatures leads to rapid cooling once you stop moving.