What is the R-value?

• A. A unit of thermal mass
• B. A measure of air leakage rate
• C. A measure of a material's resistance to heat transfer; higher R-value means better insulation.
• D. A measure of solar reflectance

Answer: (C)

R-value is a measure of a material's resistance to heat transfer. It tells you how well insulation slows the movement of heat through that material. The higher the R-value, the better the insulation’s ability to keep heat from passing through, which helps reduce heating and cooling loads and improve energy efficiency in a building. This concept is about resisting heat flow, not about how much heat a material stores (thermal mass), how much air leaks through cracks (air leakage rate), or how much sunlight a surface reflects (solar reflectance).