The tips of the feathers overlap to form a waterproof outer coat. Oil from a gland at the base of the tail helps waterproof the feathers. When a penguin preens , it spreads the oil throughout its feathers as it cleans and smoothes them. Typically, the colder the climate, the fatter the penguin. At the same time, stored fat enables penguins to go without food while they molt or brood their eggs.
Water rolls off a penguin's waterproof feathers.