The Science of Experience



How to Use SPF as a Vapor Barrier

Posted by Emillie Lee

Aug 14, 2017 9:00:00 AM

When choosing vapor barrier materials for your construction projects, you have several options. One of these is polyurethane spray foam. It's important to remember, however, that not all varieties of polyurethane foam are ideal for use in vapor barriers. To ensure safety and structural stability, it's essential that you choose the right type.


For making vapor barriers, closed-cell spray foam is by far the best choice. This is because this type of spray foam has gas bubbles trapped inside a very solid, firm polyurethane matrix. The gas bubbles are entirely trapped -- air does not move in and out of these pockets as it does in open-cell spray foam. The trapped gas bubbles in closed-cell spray foam make it a highly insulating substance and also allows it to act as a vapor barrier.

When looking for closed-cell spray foam products, keep in mind that they are also sometimes sold as "medium-density" or "high-density" spray foam. Never make the mistake of buying something labeled "open-cell" or "low-density" spray foam if your intention is to create a vapor barrier. Vapor can move right through these materials, and it will become trapped inside the air pockets.

Researchers have found that 2 inches of closed-cell spray foam is sufficient for creating a vapor barrier in cold climates. Because this material must be applied with a special applicator that combines two chemicals to yield a foam, it's important to have a licensed spray foam professional apply it for you. You can use NCFI's "find an applicator" tool to locate one in your area.

Energy rebates may be available if you use spray foam materials for your construction projects. This is because, when properly applied, spray foam insulation is a very energy-efficient and sustainable choice. Visit NCFI to learn more about this product.

Topics: Spray Polyurethane, High Density Foam, Commercial Building