Which of the following is true about the R-value of insulation?

A higher R-value indicates better thermal performance because it measures the insulation's ability to resist heat flow. The R-value is a crucial factor in determining how effective an insulation material will be in maintaining temperature within a space, whether it is keeping heat in during the winter or out during the summer. The greater the R-value, the better the material is at insulating, leading to enhanced energy efficiency and reduced heating and cooling costs.

The other options do not accurately reflect the characteristics of R-value. For instance, R-value applies to various types of insulation used in walls, roofs, floors, and even windows, not limited to just wall insulation. Additionally, R-value can be affected by factors such as settling, moisture, or degradation over time, meaning that it can decrease as insulation ages. Lastly, R-value is not the same across different materials; different insulation types have varying R-values, even when they have the same thickness. Thus, option A clearly stands out as the accurate statement regarding R-value.