What does the backing paper on batt insulation primarily act as?

The backing paper on batt insulation primarily acts as a vapor retarder. This function is important because it helps to control moisture flow within walls, ceilings, and floors. By minimizing the amount of moisture that can travel through the insulation, the backing paper plays a crucial role in preventing condensation that can lead to mold growth and damage to the building materials.

Using a vapor retarder is essential in construction, especially in climates where humidity levels are high or where there are significant temperature differences between inside and outside, as it allows for better energy efficiency and the longevity of the building structure. It is typically installed toward the warm side of the insulation, following building codes and best practices to ensure effective moisture management.

While other functions, such as providing sound barriers, fire barriers, or temperature insulation, may be relevant to the overall performance of insulation systems, they do not specifically relate to the primary role of the backing paper in controlling vapor transmission.