What does R-value measure in a building material?

R-value measures how well a building material resists the transfer of heat. It is a key factor in assessing the thermal performance of insulation materials in buildings. A higher R-value indicates better insulating properties, meaning the material is more effective at keeping heat inside during winter and outside during summer. This resistance helps improve energy efficiency and comfort in buildings, as it reduces the need for heating and cooling systems to work as hard.

The other options focus on different characteristics; for example, the speed of heat movement relates to thermal conductivity but does not capture resistance, moisture retention pertains to water management and not thermal performance, and sound insulation involves acoustic properties, which are separate from thermal resistance.