Final answer:
Sheep wool is water repellent due to the presence of lanolin, an oily substance that coats the fibers. The crimped structure of the fibers creates air pockets for insulation, and the scales on each fiber help in shedding water. These properties make wool garments, such as Scottish tartans, warm and weather-resistant.
Step-by-step explanation:
Sheep wool is water repellent and prevents the cold rain and snow from penetrating to the sheep's skin due to the natural oils known as lanolin that are present in the wool. This lanolin, combined with the wool fibers' unique structure, makes wool one of the warmest fabrics, retaining its warmth even when wet. Furthermore, the crimped nature of wool fibers creates tiny air pockets that trap air, providing additional insulation and helping to keep the sheep warm in harsh weather conditions.
In addition to wool's repellent qualities provided by lanolin, the scales on the surface of wool fibers are oriented in one direction, which helps to shed water. Moreover, when wool is woven into clothing as seen in the traditional Scottish tartan, it maintains these insulating properties, creating garments that are exceptionally good at keeping humans warm in cold climates.