Description & Characteristics. Cirrus clouds have a distinct look relative to the other nine cloud types. Because cirrus clouds are made of ice crystals, they look different than your typical puffy cloud shape, and can take on a number of different forms that resemble spider webs, fish skeletons, mares’ tail, or hair-like commas. If you’re observing a cloud that’s fibrous in nature, there’s a strong chance you’re looking at a cirrus cloud.
But all cirrus clouds don’t have that distinctive, fibrous shape. They can also be found clumped together (cirrus spissatus), be entangled (cirrus intortus), and can look not quite as majestic when you spot them closer to the horizon. Because of their ice crystal composition, cirrus clouds are also capable of various optical phenomena such as sun dogs and cloud iridescence.
Though human-formed, condensation trails from aircraft can become cirrus clouds in the technical sense (cirrus homogenitus), created as a result of jet exhaust in cold temperatures found in the upper parts of the troposphere.