In insulation, what does R-value indicate?

• A. Moisture permeability
• B. Thermal expansion coefficient
• C. Heat transfer rate; higher values indicate faster transfer
• D. Thermal resistance; higher values indicate better insulation

Answer: (D)

R-value measures how well an insulation layer resists heat flow. It tells you how strong a barrier the material is against heat moving between indoors and outdoors. The higher the R-value, the better the insulation, meaning less heat transfer for a given temperature difference. In practice, this slows down heat loss in winter and heat gain in summer, improving energy efficiency. When you stack multiple layers, you add their R-values to get the total resistance of the assembly.

Moisture permeability isn’t what R-value measures, so it’s not about how moisture moves through material. The thermal expansion coefficient deals with how materials change size with temperature, not heat flow resistance. And heat transfer rate describes how much heat actually moves, which goes down as R-value goes up; higher R-value means slower transfer, not faster.