On the mountain, you constantly alternate between exertion and stillness. The baselayer wicks away sweat from the ascent, preventing you from getting chilled in wet clothes at the belay station or on the summit.

The mid-layer retains heat within the system and wicks moisture away from the outside. In mountaineering, it must move with you: on the rock, under the climbing harness, and under the backpack straps.

The insulation layer is for all moments of inactivity: belay stations, summit rests, and breaks in the weather. It retains heat when your body is no longer generating it and is small enough to always fit in your backpack.

The top layer is your protection against wind, rain, and snow. On the mountain, it determines whether a change in weather remains an inconvenience or becomes a problem, especially where the return journey takes less than five minutes.

In mountaineering, a single pair of trousers replaces the entire layering system for the legs. They must withstand the high strides on the rock face, fit comfortably under the climbing harness, and be robust where rock, scree, and backpack wearers put stress on them.