Which is a characteristic of Class III vapor retarders?

Class III vapor retarders are characterized by having a perm rating that is greater than 1 perm and less than or equal to 10 perms. This classification indicates that water vapor can pass through these materials at a limited rate, providing a moderate level of moisture control. Proper understanding of this vapor retarder type is essential, especially in construction and insulation practices, as it plays a vital role in managing indoor humidity levels while allowing some moisture to escape, which helps in preventing issues such as mold growth.

Recognizing the specific perm rating helps inspectors and builders select the right materials for maintaining a balanced moisture level in various building applications, particularly in areas where moisture control is critical.