A flash of orange streaks across the meadow – a red fox, like a starburst in the snow. Its fur shimmers in the early morning light, and I, bundled in my winter layers and still shivering cold, envy the fox’s luxurious coat.

At its simplest, hair – or fur – keeps mammals warm by trapping heat close to the skin. Fur can also repel water. A careful look at winter pelts reveals that not all fur is the same. Long strands of bristle-like fur, known as guard hairs, make up the outside surface of many species’ coats. This fur often gives the animal its color and pattern. Under the guard hairs, thick, wavy underfur increases the coat’s surface area and traps warm air against the body.

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