How is a vapor barrier rated?

A vapor barrier is rated based on its perm values, which indicate its permeability to water vapor. The perm rating measures how much moisture can pass through a given area of the material over a specific period. This rating is crucial in understanding how effective the vapor barrier will be in preventing moisture transfer, which can lead to issues like mold growth or structural damage in various applications, especially in construction and landscaping.

Choosing a vapor barrier with the appropriate perm value is essential for maintaining the desired moisture levels in a building or landscaping project. The lower the perm value, the less vapor the material allows to pass through, making it more effective as a vapor barrier in applications where moisture control is critical.

While weight, thickness, and material type may play roles in the selection and application of a vapor barrier, they are not the defining factors in how a vapor barrier is rated in terms of its effectiveness in controlling moisture movement. Instead, the perm values provide a quantifiable measure that directly correlates with the barrier's performance.