From wet and cold Norway: truly waterproof clothing does exist, but it is of course equally waterproof both ways. So unless you bike very slowly and genteelly you will get damp no matter what. It's also so stiff as to make biking uncomfortable. I have a decent softshell jacket for dry/damp riding and a more waterproof one for damp/wet riding, but I avoid downpours as much as possible. And if I get caught in one I ride as fast as humanly possible to avoid hypothermia.