Baleen (also called whalebone) is a substance made of keratin and is therefore stiff but somewhat elastic. Whalebone is a modification of the epidermis. A bony mineral, hydroxyapatite , is also present in baleen in small amounts, along with traces of manganese, copper, boron, iron, and calcium.

"Baleen" is an Early Modern English word meaning "whale". It derives from the Latin balaena and is related to the Greek phallaina, both of which also mean "whale".

Baleen makes up baleen plates, which are arranged in two parallel rows that look like combs of thick hair; they are attached to the upper jaws of baleen whales . Whales use these combs for filter feeding.

Depending on the species of whale, a baleen plate can be 0.5 to 3.5 metres (2 to 12 feet) long. Its hairy fringes are called baleen hair or whalebone-hair. Baleen plates are broader at the gumline (base). The plates have been compared to sieves or Venetian blinds.

Sometimes "baleen" is misused to mean "baleen plate." Baleen plate was formerly used in buggy whips and parasol ribs, and to stiffen parts of women's stays and dresses, like corsets. Its function has now been replaced by plastic. It was also formerly believed that baleen plate could be obtained from whale fins.

Further reading

• St. Aubin, D.J, R.H. Stinson and J.R. Geraci 1984. "Aspects of the structure and function of baleen, and some effects of exposure to petroleum hydrocarbons". Canadian Journal of Zoology 62: 193-198