In article ,
Peter Clinch wrote:

Physics is not mocked. What I said is correct. You may well
believe in Maxwell's demon, but there's no such animal.

Once Goretex gets saturated, the surface tension no longer blocks
water from passing through, and it is no longer waterproof.

Gore have a ridiculous guarantee, "guaranteed to keep you dry". A
classic case of the large print giveth and the small print taketh away,
but in this case the small print points out the foundation to the claim
is a hydrostatic head well in excess of that considered to be
"waterproof" (MOD say 800mm, outdoor industry reckon 1m).

And that is hydrostatic head, which will be maintained whether or not it
is "saturated".

Why? What's the physics behind that? Its claims are nonsense (a
water molecule is NOT much larger than a steam molecule), and my
understanding is that the hydrostatic head is due to hydrophic
material.

XCR has a measured HH in excess of 4m IIRC, so (a) it's
difficult to see how you can apply that in testing without "saturation"
and (b) percolation rate would be zero /or Gore would be sued left,
right and centre over their fraudulent guarantee/.

Not really. Holding up a few metres of water on one side is NOT
saturation, and I am not disputing their claims. But once it gets
saturated, then there is liquid water both sides, and the surface
tension effect gives way to percolation.

I have measured this effect for several fabrics, including Goretex,
and it occurs for that as much as anything else. However, I never
managed to get more than a certain amount of dampness through the
Goretex, so all I could be sure of was that the percolation rate
was non-zero (but negligible). What I can't be sure is how much
would get through with the pumping caused by footwear and clothing
movement.

Once Goretex gets covered with water on the outside, saturated in
any other way, or it gets colder than the dewpoint of the water
vapour inside, it ceases to be breathable.

That certainly does appear to be the case. Same goes for pretty much
any other waterproof/breathable fabric, of course.

Obviously - the same physics applies.


Regards,
Nick Maclaren.