We have been wearing these thermal bibtights now for three winters, and they have definitely become a can't-leave-home-without-them item in our riding wardrobe.
Nano technology has been applied to render the surface hydrophobic, the theory being that any water that falls on them beads up and rolls off. While they are excellent in drizzle, don't go buying assuming they are waterproof - they aren't. We find that any direct splashes easily penetrate (there is no physical barrier to stop them sluicing through) and heavy rain quickly soaks in.
Even discounting anything more than a light rain resistance, you are still left with a fantastic quality, close fitting pair of warm bibtights that hold their shape and fit well even when soaking. The seatpad is good for all-day riding, never causing us any problem even in the grimmest of conditions. One of our testers is actually on their third pair, but the first pair are still going after three years of hard use, only showing signs of wearing out now.