Question

Why is a dry, fluffy coat a better insulator than the same coat when it is wet?

Short answer

Question: Explain the difference in insulation properties between a dry, fluffy coat and a wet coat, focusing on the role of trapped air and water in thermal conductivity.

Step-by-step solution

Introduction to Insulation

Insulation is the process of preventing heat transfer. In the case of a coat, it keeps the body warm in cold conditions by keeping the heat produced by the body from escaping to the surroundings. Thermal conductivity plays a significant role in insulation. Lower thermal conductivity means better insulation properties.

Role of Trapped Air in Insulation

A dry, fluffy coat is a good insulator due to the presence of tiny pockets of air trapped within the coat's fibers. Air is a poor conductor of heat, which means it doesn't allow heat to pass through it easily. These air pockets help to reduce the heat transfer, keeping the body warm.

Effect of Wetness on Insulation

When the coat becomes wet, the air pockets get filled with water. Since water has higher thermal conductivity compared to air (from 0.58 W/m·K to 0.6 W/m·K for water vs 0.025 W/m·K for air), heat transfer is more efficient in the wet coat. As a result, the coat loses its insulation properties, and the body loses heat more quickly.

Comparing Dry and Wet Coats

In summary, a dry, fluffy coat is a better insulator than a wet coat because the air trapped in the coat provides better insulation due to its lower thermal conductivity. When the coat is wet, water replaces air in these pockets, resulting in higher thermal conductivity and poor insulation.