What aspect does the U value measure in insulation materials?

The U value is a crucial measurement in evaluating insulation materials, as it quantifies the thermal conductivity of a material. Specifically, it represents the rate of heat transfer through a material, indicating how well it prevents heat from escaping or entering a building. A lower U value signifies better insulation performance, meaning less heat loss or gain, which ultimately contributes to energy efficiency and improved thermal comfort in indoor spaces.

In this context, while resistance pertains to how well a material resists heat flow, it is the U value that directly measures the actual thermal conductivity, providing a clearer picture of how effective insulation will be in practice. Thus, the focus on thermal conductivity aligns directly with the purpose of the U value in assessing insulation efficiency and suitability for various applications.