Which material is typically rated by an R-value to indicate its insulating performance?

• A. Wood
• B. Brick
• C. Glass fiber insulation
• D. Steel

Answer: (C)

R-value measures how well a material resists heat flow; the higher the R-value, the better the insulation. Glass fiber insulation is designed specifically to impede heat transfer, using air-filled glass fibers that slow down heat flow and provide a high R-value per thickness. That’s why it’s the material most commonly described by its R-value in building projects. Wood and brick do offer some insulation, but their performance isn’t standardized by a single R-value in the same way, and steel conducts heat readily, offering little resistance on its own.