Water resistance is not the only feature we should look for in outdoor clothing. Equally important are breathability and vapour permeability, which indicate how effectively your clothing (jacket, pants, sweatshirt, etc.) can wick body vapours away from the body and into the surrounding environment.
Breathability and vapour permeability - why are they important?
If the clothing was not breathable, or if it was only insufficiently breathable, it would mean that during physical activity you would start to "bath" in your own sweat over time. If you keep this garment on for a long time, you could start to overheat underneath, which could be potentially dangerous. On the contrary, the moment you would take off your clothes, you can get really cold and catch again some disease.
With outdoor clothing, it is expected that you will actively move in it, so breathability and vapour permeability should be a matter of course. Different types of textiles naturally have different qualities in this regard, with many manufacturers constantly developing and improving their proprietary materials. In this case, those are membrane materials, which, in terms of breathability, show the best properties. However, they are well followed by, for example, softshell.
What is the difference?
And what is the difference between breathability and vapour permeability? In principle, these are very similar quantities, but they are defined slightly differently. Breathability is defined as the fabric's resistance to constant evaporation of moisture. The lower the value we measure, the more breathable the material is (perhaps it seems paradoxically at first glance), the better it "breathes". In this case, the value is given in the so-called RET (with the formula Pa.m2/W).
On the other hand, for vapour permeability, the higher the better. The unit of vapour permeability is g/m²/24 h; this means that this number indicates how many grams of moisture a square meter of the given fabric can normally pass through in 24 hours.
A RET value of 6 or more is very good for breathable clothing and corresponds to a vapour permeability value of 20,000 g/m²/24 hours or more. On the other hand, with a RET value above 20 (and vapor permeability below 5000 g/m²/24 hours), it is practically impossible to talk about outdoor clothing.
Many models of outdoor clothing - we are mainly talking about jackets here - are equipped with ventilation holes (for example in the armpits) in addition to high-quality breathable materials. As far as breathability is concerned, these vents significantly help the material.