Spermaceti is a waxy substance found in the head of the sperm whale. It is primarily composed of cetyl palmitate and has a unique ability to change density with temperature, which helps the whale control its buoyancy while swimming in the ocean. Historically, spermaceti was highly valued for its use in candles, cosmetics, and lubricants. The substance was harvested during the whaling industry, leading to significant declines in sperm whale populations. Today, spermaceti is less commonly used due to the decline of whaling and the development of synthetic alternatives.