>>2642168Well, yes and no. The typical claim is that "the fibres swell up and block water". That's true to an extent, but it also means the cotton soaks in water, which eventually seeps through and brings with itself all the nastiness I mentioned.
The other part is the (usually synthetic) impregnation. Which only works so far (same thing with impregnated synthetic softshells).
Btw if the cotton gets roughed up, it absorbs water more quickly and the impregnation stops working. So that's a problem with it - it is durable, strictly speaking, but the waterproofness is not. Look at this gamsbokk bushcrafter eta proof jacket for example - they have reinforced the shoulders, because that's where wear happens and water gets in.
