PLEASE NOTE that the following information is taken from a message thread that appeared in early January, 1996, on a internet newsgroup (rec.crafts.yarn) and represents the opinions of the authors cited. It has not been verified, but is reprinted here for your own considered evaluation!
GoreTex is a membrane, not a fabric, that is water repellent. The function of the micropores, which are funnel-shaped and microscopic, is to allow water VAPOR, which is produced by the body, to escape, while liquid water molecules are blocked from getting in. The vapor molecule is smaller than the liquid water molecule, which is the scientific fact that allows this technology to work.
GoreTex is not waterproof. If you get enough water on the outside of the garment, it will leak. It's also more likely to leak after the fabric has aquired a film over it from skin oils or from detergents.
For any questions or to request a brochure, call 1-800-431-GORE.
I am in no way affiliated with W.L. Gore and Associates, I simply own a lot of products that contain GoreTex protective membranes. I spend a lot of time camping, in the rain or snow, and have had to rely on them to keep me dry. They really work. (By the way, GoreTex fiber was chosen by NASA for use in spacesuits.)
The original question was whether or not Gortex is _waterproof_. It's not. It's water resistant. The local search and rescue people tell me that it's lousy if they're doing a search in the woods, because after a while, the leaves and branches brushing against the jacket will eventually start forcing water back through. It's a two-way membrane, and is susceptable to mechanical pressure.
The Japanese use monolithic membranes in ski wear and aerobics wear, and it works just fine. In many ways, it's better than Gortex, because it has no pores, which means it really is waterproof.
Both my husband I have done slave labor for NASA Ames, researching... space suit design. The current shuttle suits don't use Gortex, unless it's part of the liquid cooled garment (LCG). Since the LCG sits against the skin, *under* the air bladder layer, it'd only be of moderate use. Having worn one of the actual suits, I can tell you that you *need* an LCG, because otherwise you'd sweat to death in the rubber air bladder layer. Gotta love feeling like the Michilan Man. ;}
If you're talking about the space station suit designs, be aware that no one design has actually be approved yet, and _none_ of them have actually been into space yet.
We were looking at monolithic membranes for mars environment suits, because the material is airtight and can be used as the air bladder layer and _still_ pass sweat out. It'd be a big improvement over the current setup.