When batt insulation is installed, what type of vapor retarder is commonly used?

The commonly used vapor retarder with batt insulation is typically a 6 mil polyethylene. This thickness provides an effective barrier against moisture while remaining flexible and easy to work with during installation. A 6 mil thickness is generally considered sufficient to prevent moisture from passing through the insulation in most residential applications.

The choice of 4 mil polyethylene might not provide adequate protection in areas with higher moisture levels, while 8 mil or 10 mil options may be unnecessarily thick and could hinder proper installation or create additional costs without significant benefits in typical residential contexts. Thus, the 6 mil polyethylene is often the preferred standard for ensuring optimal performance and efficiency in insulation applications.