How does open cell spray foam insulation differ in terms of moisture permeability?

Open cell spray foam insulation is characterized by its ability to allow moisture to pass through it. This permeability means that while it provides thermal insulation and helps to reduce air infiltration, it does not completely block the movement of water vapor or liquid water. This property is particularly advantageous in certain applications where moisture management is crucial, such as in humid climates or areas where condensation is a concern.

In terms of its structure, open cell spray foam contains a significant amount of air within its cells, which facilitates moisture permeability. This allows the material to absorb some moisture and release it, helping to moderate humidity levels within the building envelope. It is distinct from closed cell spray foam, which acts as a more restrictive barrier to moisture and air.

In contrast, options that suggest it is water-resistant or acts as a complete vapor barrier do not accurately represent the behavior of open cell spray foam. While it provides some resistance to moisture, it does not prevent water from penetrating the material completely. Additionally, stating that it prevents airflow misrepresents its function, as open cell spray foam is specifically designed to allow a degree of air movement while still providing insulation.