What is the function of a vapor barrier in insulation?

A vapor barrier plays a crucial role in insulation by preventing moisture ingress. Moisture can lead to a variety of issues within insulation systems, including mold growth, wood rot, and reduced insulation performance. The presence of moisture can compromise the effectiveness of insulating materials, lessening their ability to resist heat transfer. By acting as a barrier, it minimizes the movement of moisture from the exterior environment into the insulated spaces, helping to maintain the thermal integrity of the structure and the efficiency of the heating or cooling systems.

In this context, the function of enhancing heat conductivity would be contrary to the purpose of insulation, which seeks to resist heat flow. Additionally, a vapor barrier does not act as a conduit for refrigerants, since refrigerant lines serve a different purpose in a cooling system. Lastly, while a vapor barrier may have some effect on air movement, its primary function is not to regulate airflow but to limit moisture, making the prevention of moisture ingress its main role in the overall insulation system.