Spermaceti and Sperm Wax; the main reasons for the massive hunting of Physeter macrocephalus in the industrial era. Found in the Spermaceti Organ and the Junk (another organ adjacent to the Spermaceti Organ, see image).
Diagram showing the Spermaceti Organ and Junk (from WikiCommons).
Spermaceti was so prized due to its odourless and tasteless nature, which made it useful as an ingredient for cosmetics as well as use as a lubricant or in the leatherworking industry. Another reason that spermaceti was so valued was because it burns without smoke and was widely used in candles. So much so infact that the unit candlepower was defined by the light of one standardised pure spermaceti candle.
Spermaceti has two possible uses to P. macrocephalus. The first is as a focusing agent for P. macrocephalus’ sense of echolocation; which explains the lens-shaped sacs in the Junk. Another possible use is as a buoyancy aid, this because spermaceti can be either positively or negatively buoyant in water depending on its state. For instance when solid, spermaceti will sink; however when heated it will float. Given the extreme dives undertaken by P. macrocephalus, it is likely that this property of spermaceti is exploited for this purpose. That being said there are no structures in place for the heating or cooling of the spermaceti within the head.