Why a rain jacket is mandatory and how the 3-to-4-layer system reliably keeps you warm and dry on the mountain, no matter what the weather does.
Why are you freezing at the summit when it was T-shirt weather in the valley? The honest answer: for every 100 meters of elevation gain, temperature drops roughly 0.6°C — at 1,500 meters that's already almost 10 degrees colder, plus wind. Clothing on the mountain isn't a style choice, it's safety gear.
The tool for handling that is the layering system: three to four layers that together cushion every kind of weather — heat, cold, wind, rain. Each layer has exactly one job, and the system only really works once they play together. Here's how to layer correctly, and why some pieces of gear aren't optional.
The bottom layer has one job: move sweat away from your skin. Wet skin cools many times faster than dry skin. When you stop at the summit, a good base layer stops you from continuing to sweat and then chilling down. Use only synthetic fiber or merino wool — never cotton.
This layer traps the air your body has warmed. Fleece has an excellent warmth-to-weight ratio. For summit breaks or sudden cold snaps, also pack a light "puffy" (down or Primaloft jacket) — packed down, it's roughly the size of your palm.
The rain jacket is your most important barrier against rain, snow, and wind. Even on brilliantly sunny days, local thunderstorms or cold fronts can build fast in the mountains. A good hardshell is wind- and waterproof, but thanks to its membrane (a microporous layer built into the fabric), it lets water vapor escape from the inside — so you're not trapped in your own sweat, while rain still stays out.
The best system is useless if you don't actually use it. Rule of thumb: dress so you feel slightly cool as you set off — you'll warm up once you're moving. Start sweating, and it's time to shed a layer in good time. On breaks, put your insulation jacket on immediately, before you even feel cold. You'll likely make this adjustment several times over the course of a tour — that's normal, not a sign you packed wrong.
A weather collapse can push temperatures into the single digits or below within minutes. In an emergency, put on every layer you have and add a bivy bag or emergency blanket against wet and cold. Make sure each layer fits a bit looser than the one underneath — otherwise you cut off the air circulation that's supposed to keep you warm. You'll notice early hypothermia first in your fingers, toes, ears, and nose, since blood flow gets restricted there first.
Always pack light gloves and a beanie or headband, even on seemingly easy high-summer tours. You lose an enormous amount of heat through your head — and gloves also protect against cuts from sharp ice edges if you slip on an old snow patch. Together, these items weigh barely more than a snack bar and take up almost no space in your pack. Small, light, priceless when it matters.
Cotton soaks up sweat like a sponge and dries extremely slowly. Wet cotton sits cold and clammy against your skin, continuously pulling heat away from you — the exact opposite of what you need on the mountain.
The rain jacket always belongs in your pack, no matter how short the tour — weather can turn fast. Mid layer and extra insulation depend on altitude and season, but they don't need to be worn constantly.
As soon as you feel yourself starting to sweat — not once it's already running down your back. Stop briefly, take off the layer, keep moving. It costs you two minutes and saves you from chilling later.
Switch to a dry spare pair immediately if you have one — wet gloves chill your fingers faster than no gloves at all. That's why a dry backup pair belongs in every pack once it gets colder or wetter.
A softshell breathes better but is only water-resistant to a point — in sustained rain, you'll eventually get soaked through. For tours with real weather risk, a fully waterproof hardshell belongs in your pack; the softshell works better as an extra mid layer in dry, windy conditions.
Packing a Backpack for Day Hikes