The Penguin feathers, also called as plumage, are waterproof. They keep penguins dry underneath, even while the birds are swimming. If penguins don't keep their plumage in very good shape, they don't stay waterproof. So penguins spend several hours a day preening, or caring for their plumage. Penguins use their beaks, flippers, and feet to preen. For extra protection in the water, penguins spread oil on their plumage. The oil comes from a special gland near their tail plumage.

Penguins shed their plumage because they become worn and damaged. When penguins shed their old plumage and grow new ones, it is called molting. Penguins molt once a year. Penguins always molt on land or on ice. Until they grow new waterproof coats, they can't go back into the water. And the water is where they need to go to find food.

Sometimes penguins might have to go for more than a month without food while they molt. To prepare, penguins eat as much as they can during the weeks leading up to the molt. Eating so much helps them add fat to their bodies. The penguins live off the fat while they grow new plumage.