Why is the description "undercoat" important for understanding rabbit fur?

The description "undercoat" is crucial for understanding rabbit fur, primarily because it affects the insulation properties of the rabbit's coat. The undercoat consists of fine, soft hairs that sit beneath the outer layer of fur. This layer plays a significant role in regulating temperature, keeping the rabbit warm in colder conditions and cooler when it's hot. The quality and density of the undercoat can vary significantly among different rabbit breeds, influencing their ability to maintain body heat and affecting their overall health and comfort.

While the length of the fur, the primary color, and the identification of age may be relevant aspects of rabbit fur, they do not pertain to the effectiveness of insulation, which is critical for a rabbit's well-being in varying climates.