What is perm rating of typical 15?

The perm rating of a typical 15 refers to a measure of the water vapor permeability of a material, indicating its ability to allow moisture to pass through. A perm rating of 15 suggests that the material has a moderate permeability level, allowing for some moisture transfer while still providing a degree of moisture resistance. This rating is often used in building materials, such as insulation and vapor barriers, to determine their suitability for specific environmental conditions.