If it were more affordable, I would buy enough Ultra Ever Dry to coat my umbrella. My umbrella already does a good job of keeping the water off me, but it would be even better if, once I step under cover, a single shake would leave the umbrella dry as a bone. No need to cover it in a plastic sleeve to keep it from dripping on the floor, no need to open it inside to dry out for several hours and, perhaps most importantly, I could fold it up and put it back in my bag on public transport immediately. That would be a really big benefit, because I've left at least one umbrella on the train before, simply because I had to keep it away from my bag while it dripped. If it could hardly help but keep completely dry, there would never be any need to keep it separate ever again.
Mokalus of Borg
PS - There may be similar hydrophobic coatings that are more affordable.
PPS - The question is why umbrellas aren't manufactured hydrophobic in the first place.