Which statement correctly compares R-value and U-value in insulation performance?

• A. R-value measures resistance to heat flow (higher is better for a given material)
• B. U-value measures weight
• C. R-value measures heat transfer rate
• D. U-value measures resistance

Answer: (A)

R-value is a measure of how strongly a material resists the flow of heat. The higher the R-value, the more the material slows down heat transfer, so for a given material, a larger R means better insulation. U-value measures how much heat passes through a material or assembly per unit area and per degree of temperature difference; it’s a measure of heat transfer rate, with lower values indicating less heat loss and better insulation. In practice, R and U are inverses of each other for a simple, single material, though real assemblies can be more complex with multiple layers. So the correct statement is that R-value measures resistance to heat flow (higher is better for a given material) and U-value measures the rate of heat transfer. The other ideas—U-value measuring weight, R-value measuring heat transfer rate, or U-value measuring resistance—don’t fit.