Penguins are designed for life in the sea. Some species spend as much as 75% of their lives in the water. (They lay their eggs and to raise their chicks on land.) Heavy, solid bones act like a diver's weight belt, allowing them to stay underwater. Their wings, shaped like flippers, help them "fly" underwater at speeds up to 15 mph. A streamlined body, paddle-like feet, insulating blubber, and watertight feathers all add to their efficiency and comfort underwater. They also have a remarkable deep-diving ability.