Gore-Tex the membrane is waterproof.
The idea behind Gore-Tex is that expanded PTFE results in a membrane the pores of which are many times smaller than liquid H2O and many times larger than gaseous H2O.
So, liquid H2O cannot physically pass through Gore-Tex, and gaseous H2O readily can.
Issues:
1). Seams. They need to be sealed. The better the seam seal the longer stuff stays waterproof.
2). Gore-Tex degradation. GT is a membrane. To the extent it is protected by exterior and interior layers, it will remain intact and therefore waterproof.
3). Profuse interior moisture. This is often my challenge. Interior moisture cannot escape through the GT membrane if it is liquid, i.e., sweat. Thankfully, you can turn a whole LOT of sweat into gas, as anyone sweaty who has taken off a garment in cold weather can attest. But, I tend to overwhelm the membrane with too much moisture ... I create it faster than it can a) turn to gas, and b) pass through the membrane.
This is the proverbial "internal storm."
A couple of things:
1). I have seen some discussion about exterior layers "wetting out" and purportedly inhibiting moisture transfer through GT membrane.
The opposite is true, especially if it's cold out. Cold water on the exterior of the GT membrane will greatly enhance the transfer of moisture from the interior.
2). The "feeling" of being wet when wearing a GT shell.
Numerous times I have been in prolonged rainstorms wearing a GT shell and felt that, after a while, my shoulders were getting wet. The feeling was unmistakable.
Invariably, at least with my shell, when I later took it off, the undergarment was dry. I finally tried it with a t-shirt under my shell during a rainy round of golf, and after hours in the rain, the t-shirt was dry under the shell.
What happens is that the cooling effect of evaporation occurring on the other side of a very thin shell can make you feel wet. It is not as bad as actually being wet, but evaporation will still chill you. Since the shell is hanging from the shoulders and the membrane is therefore very close to the skin there, the "feeling" of evaporation, i.e., cold wetness, can be felt through the shell after a while.
The answer is a layer of insulation. I like fleece.
3). The greater the discrepancy between interior and exterior temperature, the more readily moisture will transfer.
Proper Gore-Tex membrane is waterproof. Stuff that truly leaks does so for other reasons. Internal moisture is by far more likely to be the culprit if you are wet wearing GT. Sometimes you can feel wet, but really are not.
