12

While reading this question, another one came to my mind:

Last summer on a mountain hut some guy told my packing newspaper in Gore-Tex (or any similar) shoes wouldn't be good for their breathability.

The explanation seemed to be plausible: Because Gore-Tex is working like a funnel (cone) letting steam out, but no water in, there is a 'working direction'.

If you put newspaper in your shoes, the newspaper would suck the moisture. BUT from outside to inside. So obviously the opposite direction of the Gore-Tex 'working direction'. This guy said it's like pressing water from the wrong side through a funnel and this could (or would) harm the effect of the Gore-Tex.

But everywhere you go, people plug newspaper in there shoes to dry them faster.

So was this guy right or wrong? Does plugging boots with newspaper kill their Gore-Tex effect?

My first thougt was, maybe the newspaper is only sucking the moisture from inside the Gore-Tex layer?

  • so, you should not wear socks either, as the fabric will suck the rain from outside the shoe? – njzk2 Dec 16 '15 at 16:41
16

I would say that this guy at the hut was plain wrong.

As far as I'm concerned, the working principle of the Gore-Tex membrane is gradient-driven. That means, the membrane itself (if you consider only the membrane and ignore the layers it is sandwitched in) does not have any physical or chemical preference to transport moisture into a certain direction. Instead it is built in a way, that

  1. water cannot pass it while vapour can and
  2. the vapour is pushed through the membrane by a difference in vapour pressure between its in- and outside, i.e. a combination of temperature and moisture difference.

Therefore what is "inside" and "outside" to the membrane is basically defined by the local conditions on both its sides. That does also mean, that reversing the conditions – i.e. drying the inside of the boot while the leather or fabric on its outside is still wet – could make the membrane work in the opposite direction and dry the outside through the membrane and the inner fabric. That would in the worst case increase the time needed to dry your shoes but not damage the membrane. Even if you consider other breathable fabrics, where the fabric itself contains a physical-chemical preference to transport water vapour into a certain direction (Sympatex for example), those will not get physically damaged when moisture is driven through in the "wrong" direction, it just takes more "force", i.e. a higher gradient to do so. For both membrane types, to really harm their function, you have to physically work them by repeated mechanical strain.

In addition, I doubt that a newspaper is able to create a strong enough vapour pressure gradient to "suck" the moisture from the boot's outside through the membrane to the inside. So I'm quite sure that your idea of the newspaper only drying the inside is correct.

But you should of course after some time remove or replace the wet newspaper from the inside. Otherwise you won't have won anything since the paper sucked the moisture from the boot but then kept a neat little atmosphere of dampness in the shoes which is the best way to make all kinds of bacteria feel well in there and make it a place of permanent bad smell...

  • +1 Really good answer. Without the paper your boots need very long time to evaporate all the water from the wicked materials (synthetic and leather). People use the dry paper so that the water can diffuse from wet to dry. As mentioned when the water is mostly absorbed (which won't take too long) you should replace the paper or if the inner fabric of the boot is dry enough, remove it. The rest of the drying will be done by air circulation and heating. – Wills Dec 16 '15 at 12:25
5

Your final sentence is correct. The newspaper will wick water from internal fabric, but it will not pull water back through the Gore-Tex layer. It only allows water vapour to pass through.

You actually need quite a head of pressure to force water through Gore-Tex, otherwise it would leak when you walk through a river, for example.

The hiking boots my family has are all Gore-Tex, and we use newspaper after any wet hikes, and it works perfectly.

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