Underfur is the soft, dense layer of fur found beneath the outer coat of many mammals, including dogs, cats, and rabbits. This layer helps to insulate the animal, keeping it warm in cold weather and providing some protection against moisture. Underfur is typically shorter and finer than the outer fur, which is often coarser and longer. The presence of underfur varies among species, depending on their habitat and climate. For example, animals living in colder regions tend to have a thicker underfur to better retain heat. In contrast, those in warmer climates may have less underfur, allowing for better temperature regulation.