Which statement best describes R-value?

• A. R-value measures thermal resistance; higher means less heat flow.
• B. R-value measures heat transfer rate; higher means more heat loss.
• C. R-value equals U-factor.
• D. R-value indicates vapor diffusion rate.

Answer: (A)

R-value measures how well a material resists heat flow. It is a measure of thermal resistance, so a higher R-value means the material provides more resistance to heat transfer, leading to less heat crossing it for a given temperature difference. In other words, heat transfer rate is inversely related to R-value: increasing R-value reduces heat flow. R-value and U-factor are related as U = 1/R, so they’re connected but not the same thing. R-value isn’t about vapor diffusion, which concerns moisture movement rather than heat. So the best description is that R-value measures thermal resistance, and higher values mean less heat flow.