How do oily feathers help the emperor penguin?

The emperor penguin's feathers are not oily. Emperor penguins have three layers of feathers that provide them with excellent insulation against the cold Antarctic temperatures. The outermost layer is short, stiff and black, while the second layer is longer and downy. The third layer is a layer of subcutaneous fat, which helps the penguin to maintain its body temperature. The feathers are constantly preened and replaced to ensure that they remain waterproof and insulating.