Gore-Tex is a semi-permeable membrane: a fabric, like a net, but not woven: it's formed by stretching. It's made of expanded PTFE, like a spongy Teflon (and their patent was about how to do the expansion/manufacturing). A microscope shows it's something like bone, or a net, or holey Swiss cheese. The holes in the fabric layer are much bigger than air and water vapour molecules (which therefore pass through); but smaller than liquid water droplets (which are many water molecules bound together), which therefore don't pass through (water on the fabric should stay on it, until it's brushed off or evaporates).
So Gore-Tex is:
- Semi-permeable to water vapour
- Impermeable to liquid water
It is therefore (allegedly, more or less) waterproof but at the same time 'breathable'.
Sometimes (as in my jacket) you don't see Gore-Tex. It's a middle layer, sewn in between the jacket's inner lining and outer shell. These other layers (i.e. the inner lining and the outer shell) are, principally, meant to be durable. They're woven, and have pockets etc. They also (being a water-resistant nylon fabric themselves) help to keep the sewn-in Gore-Tex from getting soaked: a sheet of water on the Gore-Tex would prevent its 'breathing'. In rain the Gore-Tex middle layer keeps the jacket's wet outer shell away from the inner lining and from my skin. In extremis (when all is soaked in very heavy rain) the Gore-Tex tries to stay water-repellent albeit no longer so 'breathable' (but in very heavy rain, I'm happy enough to be warm: and to have air inside the jacket).
I bought my jacket 10 or 15 years ago from MEC. Even if it is expensive (and it wasn't, especially - and I liked it so much that I bought duplicates as Christmas presents for my family, and they still wear theirs too), I'd consider whether it's durable and useful. My jacket does not have cycling-specific tailoring, so I can wear it anywhere/anytime when it's wet out. Also I (among other things) reckon I save $1,500/year in bus fare by commuting by bike: so amortizing that $1,500/year over two or more years can justify spending ('investing') the money, for buying a bike and clothes, and still come out ahead, relatively.
Anyway. So my jacket has a lining etc., as well as the Gore-Tex membrane hidden away as a middle layer. The inner lining of this jacket is mesh/webbing, which helps the jacket to stand off from the body. This makes it durable, and the nylon exterior shell makes it wind-proof. I regulate my heat (when cycling) by using the front zipper: up around the throat, or down to open the chest, which ventilates the jacket. There's a velcro strap at the cuffs to regulate the ventilation of the arms (which is why I avoid wearing a jacket in summer).
It used to be I think that Gore-Tex didn't manufacture clothes, but licensed the fabric to clothiers (e.g. my jacket was made and labelled and perhaps designed by Le Coq Sportif, who make sportswear). Now Gore-Tex seem to make and sell their own complete clothes? But other manfacturers presumably continue to license the fabric and use it.
There's a Gore-Tex "Paclite" fabric or jacket now, which I don't think I've seen/felt. I guess that's a single-layer jacket. I don't know whether that's pure Gore-Tex or otherwise how it's bonded to the shell (how it performs). I think it's aimed at cyclists. I don't know how good it is for cold-weather riding (mine, because it's lined and wind-proof, is good).
I'd like to find a good selection of jackets but I don't know where. Most LBS when I ask for Gore-Tex say "that's expensive" and don't stock it. I don't want to buy sight unseen because all the details matter.
Gore-Tex is still a brand and a trademark (and a company). Its patent has expired. I don't know what competing/similar products/solutions/manufacturers there are.