Their eyes are small and adapted to withstand water pressure. Their external auditory passages are narrow, leading to a minute hole on the head not far behind the eye. Humpback females are larger than the males. They are one of the few species of mammals for which this is true. The most distictive external features of humpbacks are the flipper size and form, fluke coloration and shape, and dorsal fin shape.
Flippers are quite long and can be almost a third of the body length.
They are largely white and have knobs on the leading edge. The butterfly-shaped tail flukes bear individually distinctive patterns of gray and white, and have a scalloped trailing edge. The humpback has the greatest relative blubber thickness for its size of any rorqual, and is usually second only to the blue whale in absolute thickness. Blubber thickness varies at different times of the year, and with age and physiological condition. They are highly mobile and opportunistic.