All rights reserved. Sperm whales' heads are filled with a mysterious substance called spermaceti. Scientists have yet to understand its function, but believe it may help the animal regulate its buoyancy. They have the largest brain of any creature known to have lived on Earth. Their heads also hold large quantities of a substance called spermaceti.
Why the sperm whale has a huge head
Sperm Whale | National Geographic
I know all of you are dying to get your dirty little hands on this number. Wait your turn, please. I was looking at my Visualized Physics book, reading about the measurement of light. Against my will, I imagined a 19th century sperm production facility that harvested the spunk of a bunch of criminals or moral reprobates and then daintily fashioned the would-be humans into burning cylinders of light for Victorian households.
Sperm oil is a waxy liquid obtained from sperm whales. It is a clear, yellowish liquid with a very faint odor. Sperm oil has a different composition from common whale oil , obtained from rendered blubber.
Spermaceti from Greek sperma meaning "seed", and ceti , the genitive form of "whale"  is a waxy substance found in the head cavities of the sperm whale and, in smaller quantities, in the oils of other whales. Spermaceti is created in the spermaceti organ inside the whale's head. Two theories for the spermaceti organ's biological function suggest it either controls buoyancy , or acts as a focusing apparatus for the whale's sense of echolocation. There has been concrete evidence to support both theories. The buoyancy theory holds that the sperm whale is capable of heating the spermaceti, lowering its density and thus allowing the whale to float; in order for the whale to sink again, it must take water into its blowhole which cools the spermaceti into a denser solid.