Layering Guide

You don't wear one warm jacket in winter — you manage a system of layers you can open, close, add, and shed as your output changes.

Base Layer — Keep Skin Dry

The base layer's only job is moving sweat off your skin. Wet skin in wind strips heat from your body many times faster than dry skin.

Merino wool or synthetic (polyester/nylon) — both insulate somewhat even when damp.
Fit: snug but not tight; it needs skin contact to wick.
Zip neck on top gives you instant ventilation on climbs.
Bring a spare dry base layer for camp and for sleeping.

Start slightly cold at the trailhead — you will heat up within 10 minutes.

Don't

Never wear cotton as a base layer in cold conditions.

Mid Layer — Trap the Heat

The mid layer is insulation you add and remove as effort changes. Think of it as adjustable, not fixed.

Fleece for high-output days: it breathes and insulates even damp.
Down puffy for breaks and camp: unbeatable warmth-to-weight, useless when wet.
Synthetic fill puffies: heavier, but they keep insulating when soaked — the safer winter choice.
Carry more insulation than you think you need; winter nights are long.

Shell — Block Wind and Water

The shell holds the system together: it stops wind from pumping heat out and keeps snow melt off your insulation.

Waterproof-breathable hard shell for wet snow, rain, and storm travel.
Wind shell (lighter, more breathable) for cold dry days.
Pit zips are not optional — venting is how you stay dry from the inside.
Shell pants for deep snow, wind, or any day with rain in the forecast.

Managing the System

The skill isn't owning layers — it's reading your body and adjusting before you're soaked or cold.

Vent early: open zips when you start warming, not when you are already sweating.
Pull the puffy on the moment you stop moving — heat leaves within two minutes.
Dry damp gloves and socks against your body or in your bag overnight.
Check your partner: frosting zippers, unzipping everything, or stripping layers can all be warning signs.

Why cotton kills

Cotton holds up to 27 times its weight in water and loses nearly all insulating value when wet — and in winter it never dries. A cotton shirt under a shell in freezing rain is a portable heat pump running in reverse. Merino or synthetics only, from skin out.