What is the term for the visible layer of fur that is coarser and grows over the underhair?

The visible layer of fur that is coarser and grows over the underhair is referred to as guard hair. Guard hairs serve several important functions for mammals, including protection against the elements and providing insulation. They are typically longer and more stiff than the softer underhair, which is responsible for thermal insulation. The presence of guard hair helps to waterproof the coat and contributes to the overall appearance of the fur, making it an important component of an animal's integumentary system. This layering effect, with guard hairs sitting atop the underhair, allows for both functionality and aesthetics in fur-bearing animals.