How can a type of insulation's R-value increase?

The R-value of insulation measures its thermal resistance, indicating the effectiveness of the material in preventing heat transfer. An increase in R-value can occur through the use of insulation in layers. When insulation is installed in layers, each layer adds its own thermal resistance, thus cumulatively increasing the overall R-value of the assembly. This layered approach allows for more air pockets and reduces heat transfer not only through conduction but also through convection.

In practical applications, using multiple layers can help to trap more air, which is a poor conductor of heat, thereby enhancing the insulation's effectiveness. This method also allows for flexibility in adjusting insulation levels to meet specific building codes and performance requirements.

While other methods, such as using thicker material, can also increase R-value, the primary consideration with layering is the expansion of total thermal resistance due to the combination of multiple layers of insulation, which can be more effective in certain situations.