They're pretty good stregth pvc , very stretchy and squash down pretty small compared to your average pac-a-mac.
Wore mine for one session in the morning at Cadders and didn't know i had it on.
To use one for touring might be a bit troublesom - you can't put it on when you're already leathered up... have to dress your leathers with it first, otherwise you'll need an assistant (thanks CK xx)! But once on it'll keep your top arf dry all day long.