Open Cell vs. Closed Cell Spray Foam: Choosing the Right Insulation

Spray foam insulation, also called spray polyurethane foam (SPF), is applied as a liquid that expands to fill spaces and create an insulating layer. When properly installed at the required thickness, spray foam can provide both insulation and air sealing, helping reduce unwanted heat transfer and air leakage.

The two main types are open cell spray foam and closed cell spray foam. Both can be effective insulation materials, but their density, R-value, moisture performance and recommended applications differ.

Open cell spray foam is a lower-density insulation with a soft, flexible structure. Because it expands considerably after application, it can fill irregular spaces, gaps and hard-to-reach areas. Open-cell foam typically provides an R-value of about R-3.6 to R-4.5 per inch. When installed at the appropriate thickness, it can also serve as an effective air barrier.

Because open cell spray foam is more permeable to water vapor than closed-cell foam, the overall wall or roof assembly needs to be designed for proper moisture management. Depending on the climate and application, an additional vapor retarder may be required.

Open cell spray foam may be a good choice when:

• You have enough cavity depth to achieve the required R-value.
• You're insulating interior walls or other appropriate above-grade areas.
• You want an insulation that expands significantly to fill cavities.
• Your application doesn't require the greater moisture resistance of closed-cell foam.
• You're looking for a spray foam option that's typically less expensive than closed-cell foam.

Closed cell spray foam insulation is denser and more rigid than open-cell foam. Its compact cell structure helps it provide a higher R-value per inch, typically about R-5.8 to R-6.9. The higher R-value can make closed cell spray foam especially useful where insulation space is limited. It's also more resistant to water and water vapor than open-cell foam. At sufficient thicknesses, some closed-cell products can function as a vapor retarder in addition to providing insulation and air sealing.

Closed cell spray foam may be a good choice when:

• You need a higher R-value in a limited amount of space.
• Greater moisture resistance is important.
• You need a denser, more rigid insulation.
• The project involves an application specifically approved for closed-cell foam.
• The wall, roof or floor assembly calls for reduced vapor permeability.

Closed-cell foam typically uses more material than open-cell foam to cover the same area, contributing to its higher cost.

Depending on the product and building design, spray foam insulation may be used in several areas of a home, including:

• Exterior wall cavities
• Attics and roof assemblies
• Floors above unconditioned spaces
• Rim joists
• Basements and crawlspaces
• Around penetrations and other areas where air sealing is needed

It’s important to note that not every spray foam product is appropriate for every location. For example, the requirements for an unvented attic or crawlspace can differ from those for a conventional wall cavity. Always check the product specifications and local building codes to make sure the insulation is approved for your application.

Spray foam insulation must be installed at the correct thickness and under appropriate temperature, moisture and ventilation conditions to perform as intended. High-pressure two-component spray foam installation also requires specialized equipment, personal protective equipment and procedures for controlling exposure during application and curing.

For large projects or areas such as attics, walls and crawlspaces, consider hiring a qualified insulation professional. Follow the spray foam manufacturer's installation and ventilation instructions, and make sure the finished installation complies with local building and fire codes.