CSLB Class B General Contractor's License Practice Exam

Which insulation material has the lowest R-value per 1-inch thickness?

1. Glass fiber (batts)

2. Cellulose (loose fill)

3. Mineral fiber (loose fill)

4. Phenolic (foam)

The correct answer is: Mineral fiber (loose fill)

The R-value measures an insulation material's thermal resistance, indicating how well it can resist heat flow. The higher the R-value, the better the insulation's effectiveness. Mineral fiber (loose fill), which is made from natural or synthetic minerals, typically has a lower R-value per inch compared to other commonly used insulation materials. In this case, while glass fiber batts, cellulose loose fill, and phenolic foam all have relatively higher R-values per inch, mineral fiber's composition and structure lead to its reduced effectiveness in insulation compared to those options. Therefore, it is recognized for having the lowest R-value of the given choices, making it less efficient in providing thermal resistance when compared to glass fiber, cellulose, and phenolic, all of which offer better insulating properties per inch. Understanding this helps in selecting appropriate insulation materials based on the required thermal performance for construction projects.