Woollen clothes are used in winter because wool is a poor conductor of air. Let's understand why this property of wool makes it suitable for winter clothing.

Poor Conductor of Air:
1. Insulating Properties: Wool has excellent insulating properties due to its structure. The fibers of wool have numerous air pockets within them. These air pockets create a layer of insulation, trapping warm air close to the body and preventing it from escaping. This helps in maintaining body heat and keeping the wearer warm in cold weather.

2. Reduction of Heat Transfer: Poor conductivity of air means that heat transfer through the fabric is minimized. As air is a poor conductor of heat, the trapped air pockets in wool act as barriers, reducing the transfer of heat from the body to the surroundings. This insulation is crucial in cold weather as it helps in retaining body heat and preventing the entry of cold air.

3. Retention of Moisture: Wool can absorb moisture without feeling wet. The absorbed moisture forms hydrogen bonds with the wool fibers, generating heat in the process. This heat helps in keeping the wearer warm. Additionally, the absorbed moisture does not evaporate quickly, further contributing to the insulation provided by wool.

4. Durability and Softness: Apart from its insulating properties, wool is also known for its durability and softness. The fibers of wool are strong and resilient, making them suitable for winter clothing that needs to withstand regular wear and tear. The softness of wool adds to the comfort and coziness of woollen clothes.

Conclusion:
In conclusion, wool is used in winter because it is a poor conductor of air. Its insulation properties, ability to retain moisture, durability, and softness make it an ideal choice for winter clothing. The air pockets within wool fibers prevent heat loss, keeping the wearer warm and comfortable even in cold weather.