Types of Spray Foam: Understanding Closed-Cell and Open-Cell Foams

CLOSED-CELL FOAM VS. OPEN-CELL FOAM  

If your aim is to learn about spray polyurethane foam insulation, you’re on the right page.  

Before moving forward with a spray foam application on a commercial, agricultural, or residential building, it is essential to determine whether you will use 0.5 lb./cu. ft. open-cell foam or 2.0 lb./cu. ft. closed-cell foam. When considering performance, application methods, and pricing, the differences between open-cell foam and closed-cell foam are quite significant. In our area, closed-cell foam is primarily utilized due to the harsh winters.  

Two key factors must be evaluated to differentiate between open-cell and closed-cell foam. First, let's examine the characteristics of each type of foam. Open-cell foam has minuscule cells that aren't completely sealed, making the foam permeable and capable of absorbing air and moisture. This results in open-cell foam being weaker and softer compared to closed-cell foam. In contrast, all the tiny cells in closed-cell foam are sealed, containing a gas that allows the foam to expand and effectively insulate a structure. The formulation process gives the cells specific attributes that enhance their performance.  

Open-cell spray polyurethane foam, sometimes referred to as half-pound foam, typically has a density of 0.5 lb. per cubic foot and offers an R-value of 3.5 or 3.6 per inch. On the other hand, closed-cell foam, also known as two-pound foam, generally features a density of 2 lbs. per cubic foot and an R-value ranging from 6 to 6.5 per inch.  

Open-cell spray foam has an average density of 0.5 lbs per cubic foot, providing a typical R-Value of 3.5 to 3.6 per inch. Due to its vapor-permeable nature, three inches of open-cell foam has a permeance of 16 perms and often requires a vapor retarder for interior applications. Conversely, closed-cell foam acts as a vapor retarder itself, being semi-impermeable; two and a half inches of closed-cell foam maintains a permeance of 0.8 perm.  

What are the differences between open-cell and closed-cell polyurethane foams?  

Before proceeding with a spray foam application, it is crucial to establish whether you will be using 0.5 lb./cu. ft. open-cell foam or 2.0 lb./cu. ft. closed-cell foam, keeping in mind the significant performance and application differences. Open-cell foam is generally preferred in warmer climates without harsh winters.  

In distinguishing between open-cell and closed-cell foam, the density of the foam is a critical factor. To assess density, one solid cubic foot of foam material is weighed. Open-cell foams typically have a density around 0.4 to 0.5 lb./cu. ft., whereas closed-cell foam densities can vary based on insulation and roofing applications, often ranging between 1.7 lb./cu. ft. and 2.0 lb./cu. ft. For roofing projects, contractors may use foam densities from 2.8 to 3.0+ lb./cu. ft. The higher density of closed-cell foam contributes to its rigidity.  

Additionally, polyurethane foam can be employed in decorative settings, like creating interior molding, and can be stained or painted to mimic wood grain, especially at very high densities of 30 lb./cu. ft. to 40 lb./cu. ft.  

Closed-cell foam exhibits greater resistance to water vapor and air leakage, offering increased strength and a higher R-value than open-cell foam. However, its greater density requires more material compared to open-cell foam. To determine the most suitable foam, consider characteristics like vapor control, strength, and available space to meet application needs. Open-cell foam typically uses water as a blowing agent and provides an R-3.5 value, while closed-cell foam utilizes high R-value blowing agents, offering an R-6 value.  

The factors mentioned above are crucial when deciding between closed-cell and open-cell foams, as these are the most common types of spray polyurethane foam used in building applications. Selecting the appropriate foam type is vital since using the wrong foam can be ineffective in certain applications. For instance, open-cell foam should not be employed in areas where water absorption is likely, as it significantly compromises insulation properties. Therefore, using open-cell foam below grade or in flotation applications may provide minimal thermal insulation. Closed-cell foam would be the correct choice in roofing applications or scenarios requiring maximum R-value per inch.  

Prior to deciding between open-cell and closed-cell foam, it is advisable to request application and performance information from your supplier. Understanding the type and performance of the foam before starting the job is an important discussion to have with the spray foam applicator to ensure you are well-prepared.