Modern gore Tex (and similar) shell jackets often are marketed as being 2 or sometimes 3 layer construction with the Gore Tex membrane being one of the layers. Often the outer layer isn’t actually waterproof and can soak through. If gore Tex is the main functional layer why does there have to be extra material layers facing the elements?
In: Engineering
what others have commented is mostly correct. but to add to it: Gore-Tex (and those like it) is a waterproof and (almost more importantly) BREATHABLE membrane. This means any moisture inside the jacket, like perspiration, can escape. Layering other fabric around the membrane protects it (outer layer) and/or makes it more comfortable against the skin (inner layer). the outer layer of fabric will have what’s called a DWR finish (Durable Water Repellant). It’s a hydrophobic coating (usually an oil or waxed based) that caused water to bead up and run off. This is NOT what makes the fabric ultimately waterproof—the membrane does that. Yes, it makes water bead up on the fabric and shed off, but if you were to submerge it in water without it being bonded to a waterproof membrane, it would leak. The DWRs primary purpose is to keep the outer layer of fabric from becoming saturated with water. if the outer layer of fabric gets too waterlogged, not only will your jacket now be heavier, it will suck all the heat right out of you making you feel cold. Furthermore, when the outer fabric layer gets saturated, the Gore-Tex (or other membrane) can no longer allow moisture (such as perspiration) to escape. This is a really important feature for the purpose of temperature regulation. If water is not beading up on your Gore-Tex jacket and you are wet inside the jacket, it is not the Gore-Tex failing… it’s your own sweat that cannot escape because the DWR has worn off the outer fabric.
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