Shell: what is it and how to use it in the mountains?

The mountain shell or "shell" is, without a doubt, the most important item in a hiking wardrobe.

The first question you need to ask yourself when choosing your shell is: what kind of use will I make of it?

We must ask ourselves this question immediately because not all shells have the same characteristics, which can cause their price to vary greatly.

One can say with certainty that the shell is the hiking garment where it's worth spending a bit more money, but the price, and thus the quality and technical characteristics of the product, depend heavily on what kind of hiker you are and what features you demand from your clothing.

The shell's main function is to help us during difficult moments in the mountains related to three adverse climatic factors:

• strong wind
• more or less intense rain
• the snow

For a correct choice, it is of fundamental importance to take into consideration two key factors:

• impermeability
• breathability

Our body, especially during intense physical activity, produces water vapor.

If the water vapor encounters a barrier that doesn't allow evaporation, it condenses and returns to a liquid state, giving us a wet sensation that becomes even more uncomfortable as it cools.

A garment that doesn't allow breathability, meaning the removal of water vapor from our body, even if it's waterproof, doesn't solve our problem.

How can a garment be both waterproof and breathable at the same time?

This long-standing problem was solved some years ago, with a very particular line of reasoning.

A water molecule has a diameter of about 0.2 nanometers, so to block it, you need to build a "net" with extremely tiny holes—so small they don't let water in, but simultaneously large enough to allow water in vapor form (which has molecules smaller than 0.2 nanometers) to escape. 

This ingenious, though not simple to apply, solution was achieved by creating a membrane—a very thin film produced by the expansion of Teflon—in such a way as to construct a network of conical micro-holes.

This very thin film, when bonded to the support fabric through a special process, prevents water from entering while allowing water vapor to exit, thus making the garment simultaneously waterproof and breathable.