Underfur is the soft, dense layer of fur found beneath the outer coat of many mammals, including dogs and cats. This layer provides insulation, helping to regulate body temperature and keep the animal warm in cold weather. Underfur is typically shorter and finer than the outer fur, which is often coarser and longer. In addition to its insulating properties, underfur can also help with buoyancy in aquatic animals like otters and seals. The combination of underfur and outer fur creates a protective barrier against water and harsh environmental conditions, ensuring the animal's comfort and survival in various habitats.