Baleen plates are somewhat triangular and arranged like teeth in a comb. The inner edge is frayed, and the fringes form a dense mat inside the mouth. Baleen is made mostly of keratin, a substance found in our fingernails and hair. The largest eat the smallest. Depending on the species, baleen whales also eat small schooling fishes, and a variety of crustaceans such as krill, copepods, and amphipods.
Baleen plates work like a strainer.
Baleen whales use baleen to strain food from the water. Some feed by swimming with their mouths wide open. Others open their mouths and take in huge amounts of water. When they dose their mouths, the water is forced out through the baleen, and food gets trapped in the fringe mat. After all the water is gone, the whale swallows its meal.