The waterproof pants (containing the so-called "hardshell membrane") are designed to protect you in heavy rain and snowfall while at the same time wicking away moisture from perspiration when moving outside - i.e. they keep you dry, keeping as close to the natural microclimate as possible. They are worn as an outer layer over thermal underwear or over elastic trekking pants in colder weather. You can judge the quality of a waterproof pant by two main parameters: hydrostatic head (the degree of water protection, measured in mm) and the so-called "breathability" of the fabric (the ability of the membrane to take moisture outside, measured in gr./sq.m/24h). As for the design of this type of pant, an important feature is the presence of zips for ventilation, with the best models having a zip along the entire length of the leg on the outside, making them easy and quick to put on in case of a sudden deterioration in the weather.