Gore-TEX, a lightweight, waterproof fabric made from the expanded form of PTFE
Gore-TEX and other waterproof breathable (WPB) membrane fabrics are ridiculously oversold to people who don't spend much time outside. The amount of breathability they offer is ludicrously low compared to something like unzipping a jacket zipper or pit vent. If you're moving at all, a WPB jacket means that you'll be drenched from the inside due to sweat, and all that water repelled by your jacket ends up on your pants and shoes. Then people think they need WPB head to toe, which is like wearing a big ziploc bag.I had a friend come on a hike with me wearing a three layer Gore-TEX jacket on a warm, completely clear day. I think he began to overheat with it (wearing a sweatshirt underneath) while in the parking lot, before we even got on the trail. He ended up carrying it the entire way.I used to bike commute and walk in the rain, long before even knowing Gore-TEX existed. Being warm is more important than being dry (if you're not in subzero temperatures). Wool and synthetics will keep you warm even if they're wet - I've spent a fair amount of time soaking wet but feeling fine. And stuff will dry out quickly when you're wearing it indoors.If you're a mountaineer, sure - use Gore-TEX if being cold and wet is likely going to kill you. And don't forget all the other layers. But for normal people, we don't need it.