Which of the following is an example of a class III vapor retarder?

A class III vapor retarder, such as gypsum board, is characterized by a permeance rating between 1.0 and 10.0 perms. This level of permeability allows some moisture vapor to pass through, thus providing a certain degree of moisture control without completely sealing off the wall assembly. Gypsum board is commonly used in construction for interior walls and ceilings, offering structural support while also managing the movement of moisture.

In contrast, fiberglass and foam insulation typically fall into class I or class II vapor retarder categories, depending on their thickness and specific properties. These materials can either fully block vapor movement or significantly reduce it, which does not align with the characteristics of a class III vapor retarder. Wood panels can also vary in their permeability but generally do not possess the same properties as gypsum board, making it less applicable as a class III vapor retarder.