Layering
The Three-Layer System, Explained (and Where Everyone Goes Wrong)
People freeze in €800 of gear because they treat clothing as a pile instead of a system. The three-layer model is old, unglamorous and still correct — when you use each layer for its actual job.
The jobs
| Layer | Job | Never its job |
|---|---|---|
| Base | Move sweat off skin | Warmth |
| Mid | Trap dead air | Block wind |
| Shell | Stop wind and water | Insulate |
Cold is usually a moisture problem or a wind problem wearing a warmth costume. Diagnose which, and the fix is obvious.
Base layer: sweat management
The base layer's job is to be dry, not warm. Damp fabric conducts heat away from skin roughly 25× faster than air — which is why the material matters more here than anywhere else:
- Merino wool — comfortable across a wide range, odour-resistant for days, still insulates somewhat when damp. Slower to dry than synthetic. The default recommendation.
- Synthetic (polyester/polypro) — wicks and dries fastest, cheapest, but smells after one hard day.
- Cotton — no. Cotton absorbs sweat, holds it against your skin and keeps conducting your heat away for hours. "Cotton kills" is mountain-rescue vocabulary, not a slogan.
Weight guide: 150–200 g/m² merino for active use, 230–260 g/m² for low-output cold days.
Mid layer: the air trap
This is where warmth actually lives. Fleece (100/200/300-weight), a light down or synthetic "puffy", or wool sweaters all work — the choice is about breathability vs. static warmth:
- Moving hard? Fleece or active insulation — they vent sweat vapour through.
- Standing around? Puffy — maximum trapped air, minimal breathability needed.
Two thin mid layers beat one thick one: more trapped-air boundaries, more adjustability.
Shell: the weather gate
Wind strips the warm-air boundary off your body; a shell as thin as a plastic bag stops that. Waterproof-breathable shells (see our ratings guide) handle precipitation too. The shell adds almost no warmth on a calm day — which is exactly why it earns its place on a windy one.
The four classic mistakes
- Overdressing at the start. If you're warm standing still at the trailhead, you're two minutes from sweating. Start slightly cool; the sweat you don't produce is warmth you keep.
- A shell over a soaked base. The shell traps the moisture in. Fix the base layer problem first.
- Layers too tight. Each layer compressed against the next has no air to trap. Size mids to fit over the base with ease.
- Ignoring the vents. Pit zips, front zips and cuffs are your thermostat. Adjust every ten minutes, not once per day.
A worked example (-5 °C, breezy, walking)
200 g/m² merino base → 200-weight fleece → uninsulated windproof shell. That's it. Cheaper, lighter and warmer in practice than one giant parka — because it's a system you can tune, and the parka isn't.