Does closed cell spray foam insulation act as a vapor retarder?

Closed cell spray foam insulation does indeed act as a vapor retarder, primarily due to its dense, closed-cell structure. This type of insulation has a high R-value per inch and can significantly reduce heat transfer as well as moisture transmission. The effectiveness of closed cell spray foam as a vapor retarder is influenced by its installed thickness; as the thickness increases, its ability to retard vapor movement improves. Typically, when applied at the manufacturer's recommended thickness, it provides a barrier against moisture, which is especially critical in preventing condensation within walls and roofs.

In various climates, especially those with extreme temperature fluctuations, controlling moisture movement is essential to enhance the longevity and performance of building elements. This capacity to function as a vapor retarder is one of the reasons closed cell spray foam is often recommended for use in areas prone to moisture issues, such as basements and crawl spaces.

Choices that imply closed cell spray foam does not act as a vapor retarder, or limit its effectiveness based on climate or specific applications like walls, overlook its inherent properties and the versatility it offers in different settings. Therefore, acknowledging that the vapor retarding capabilities of closed cell spray foam hinge on proper thickness lends complete validity to its classification as a vapor retarder.