Almost everybody knows the scene. You're exterior, it's rainy and you're totally wet because your coat didn't keep the water out or at least it feels like this. Often it's your own sweat that make you feel wet. The wet fabric of the jacket cannot transport your sweat out of the parka when the outer layers are wet and so you think the coat is permeable. This is the second it starts to feel nasty. If you want to avoid the situation described above you need two things: A coat that is really waterproofed and a material that is able to breath.
If you buy a coat which can't handle a good amount of water even the ability totransport your sweat out of the jacket isn't useful anymore, that should be clear. But if you have too strong waterproofed textile, the effect described in the scene above will appear. Goretex is a fabric that is made for thisintend. It's a breathable material made of different layers.
The pores of goretex are 20000 times smaller than a water drop. That's what makes the membrane really good to protect against water and additionally wind. The evaporated transudation is still able to make its way trough the material, so the coat becomes breathable. This ability of goretex is extremely important for the regulation of the human body temperature. The body tries to cool itself by sweating. But if the sweat isn't able to find its way out of the coat, this system doesn't work the right way.
There is one important thing you should take care about. The normal goretex covering layer does only work if there is a relevant difference in the temperatures of the outside world and inside the jacket. The human body temperature is around 36 degrees Celsius. As goretex needs a difference around 15 degrees Celsius it's working up to antemperature about 20 degrees Celsius, whats about 68 degrees Fahrenheit. If you need a jacket for higher temperatures you should look for special goretex fabrics with a more powerful membrane technology.
If you got your goretex coat already, there are still some things to take care about, to use your coat the most effective way. The clothes you wear under your jacket should also be able to let pass your sweat instead of absorbing it. So cotton wouldn't be the best choice, because your jacket won't be of great use if you block the sweat already with the first layer of clothes. When you're going to buy a new jacket the next time, think about all this information.
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