How to make a better raincoat with tiny "water bowls"

A FEW YEARS ago Kripa Varanasi, a researcher at the Massachusetts Institute of Technology, made the news with a ketchup bottle that could be emptied without leaving any of the ketchup behind. Instead of sticking to the bottle's interior, the sauce was repelled by it. Superhydrophobicity, as physicists call this effect, involves peppering a surface with microscopic structures that contain pockets of fluid. That reduces the area of contact between the surface and any water droplets which fall on i...