Rapha, nice but a bit pricey?

^^^^ Is it actually though?(genuine question) I know most waterproof fabrics work fine in tension like that, but the problem comes when it has something pressing against the inside of the membrane, which might be an issue with a close fitting jacket,
and, its not airtight, so it's going to let air through under pressure, not sure how that relates to normal usage

Exactly.

There is a youtube clip like this for every membrane based fabric out there. Looks very cool. But what about the capillery effect, what about sweat vapour, what about stretched areas, what about resistance to washing. etc. etc.