The Ultimate Guide to Spray Foam R Value
If you don’t work with insulation every day, you might not know the term R value or why it’s important. Natural Polymers specializes in spray polyurethane foam chemistry and we can help you understand the differences between closed- and open-cell spray foam and how it compares and outperforms other insulation options when it comes to R value.
What is an R value?
R value is the rating given to insulation and is based on its resistance to conductive heat flow. A higher R value provides better insulating performance because it has higher thermal resistance. The value rating depends on the type of insulation, density, thickness, geographic conditions of the home like temperature, moisture/humidity, even how time impacts the structure and performance (aging). It’s important to understand the difference between insulation types compared to your desired R value for the space you’re insulating.
What is the best R value of Spray Foam Insulation?
Spray foam insulation has the highest R value per inch compared to all of the other types of insulation you can choose from, and works well for both residential and commercial projects. When applied by professional installers, spray foam fills and seals targeted spaces, and the combination of high R value material and exceptional air seal provides superior performance in comparison to alternative products like fiberglass, which is packed loosely and settles over time or requires much thicker application.
A good analogy is winter coats: the latest puffer jackets combine very efficient insulation fill with high-performance wind-blocking fabrics to provide thin, lightweight but extremely warm comfort versus the old, bulky and heavy parkas of the past.
That being said, there technically is not a “best” R value since the optimal R value is situational based on where the building is located, what the climate is like, and the location of the insulation, just like the choice of coat depends on when and where you need it. You should take into account where in the home or building you’re using it and how much moisture it is going to be exposed to regularly when determining what R value you need in your spray foam insulation. Local building codes, architects, and builders can provide a starting point for determining the appropriate level of total R value you’ll need from spray foam. However, not all spray foam is equally applicable to all spaces and often it varies within the home or building. Using the wrong type of insulation in a particular location is at best minimally effective or, worse, can introduce new issues. Ask questions to make sure you understand what insulation is recommended and why. Cost is certainly a consideration but the payback on using spray foam comes from lower energy costs to heat and cool your home due to the R values. Additionally, a tighter building envelope reduces the load on the HVAC systems and in new construction can result in lower HVAC tonnage. Gather all the information to make the best decision for your home. Often a combination of insulations is recommended as the best approach.
What Is the R Value of Spray Foam, and Do R Values Differ Between Closed-Cell and Open-Cell Spray Foam<
There are two basic types of insulation—open-cell and closed-cell—and they have different R values and uses. The cells in open-cell insulation are just that, open. This makes the foam softer and more flexible. Closed-cell is made up of cells that are pressed together, so air and moisture are unable to get in, making the foam more rigid and dense. The closed cells are also filled with exceptional insulating gases which enable even greater levels of thermal resistance. These gases stay trapped in the closed cells over the life of the foam.
Open-cell insulation is a good option when you’re insulating hard-to-reach spots in your home. It also is a great option if you’re using spray foam insulation to dampen sound in an area in your home, such as within the wall between bedrooms, to increase privacy. It’s more affordable than closed-cell insulation but doesn’t insulate as well in extreme hot or cold climates.
Understanding the differences between closed-cell and open-cell spray foam can be challenging, therefore it is important to talk through the insulation options with your architect and builder to get the best insulation for the application. In some cases, an architect may use both open- and closed-cell spray foam in the same building, leveraging each for its greatest strengths and benefits, including the R values of each.
In addition to providing excellent thermal resistance and creating a tighter building envelope, closed-cell foam can add to the structural integrity of a space since it is naturally rigid. Because it’s vapor-resistant, moisture and air cannot get through, resulting in fewer air leaks and more efficient heating and cooling in the home or building, saving money in heating and cooling costs.
As far as R values go, open-cell spray foam insulation has a lower R value than closed-cell but still higher than other traditional insulations like low-density fiberglass and cellulose. The R value of open-cell is R-3.5 to R-3.7 per inch. In many cases, this R value is sufficient for the insulation requirement of certain spaces and certain geographic areas.
Closed-cell insulation varies from open-cell in that it is denser and less porous. During installation, closed-cell spray foam receives a boost in efficiency due to a tight bond and sealed cell structure, resulting in a higher R value than open-cell. Two other commonly overlooked benefits of closed-cell insulation is that it helps prevent other external allergens from getting through. With a tight reinforcement of sprayed-in-place closed cell, another preventative layer is added.
The R value of closed-cell is R-6.5-7 per inch, increasing structural integrity, noise barriers, moisture resistance, and creating an overall tighter building envelope. This makes closed-cell foam insulation a superior choice for insulating exterior walls and roofs—an option not suited for open-cell. There is a growing trend for closed-cell spray foam for new construction because it provides the highest R value and additional protection from extreme weather conditions. Due to the higher cost when using closed-cell, it is sometimes more efficient to insulate interior walls with open-cell foam and use closed-cell insulation for situations where moisture and the potential of heat and chill transference is more of an issue.
What is the R value of 2 inches of spray foam insulation, versus the R value of 4 inches of insulation?
The overall R value of spray foam insulation is based on its thickness, so the R value, for example, of 4 inches of spray foam insulation is going to be twice as high as that of two inches, and so forth.
To determine the overall R value, you multiply the per inch R value of the spray foam by how many inches you’re using. Because the R value of open-cell spray foam is R-3.5 to R-3.7 per inch, you’ll get a total R value of R-7.0 if using two inches of foam and a total R-14.0 if you’re using four. With closed-cell spray foam insulation, it will be a total of R-13.0 for two inches and R-26.0 for four.
In an attic where space is often available, many inches of foam can be applied, for example up to 6 or more inches of open-cell spray foam. Of course, in tighter spaces like a 2×6 wall cavity, you’re not always going to have the option to apply many inches of insulation, especially if you install drywall. In such a case, closed-cell spray foam can easily enable the prescribed R-21 insulation for walls in colder climate zones. In addition, it is important that the thickness of insulation also conforms to other building code requirements such as fire performance. These testing results are often very specific for the thickness of foam and should be in compliance with local building codes. Besides meeting the most difficult R-value requirements in confined spaces, spray foam provides the additional benefit of air sealing, a powerful tool for enhancing the insulation performance of the entire building envelope. As a result, spray foam insulation is excellent at reducing thermal loss through conduction and convection in homes and commercial buildings. This is one of the many reasons the demand for spray foam insulation continues to grow, especially in the residential construction and commercial building segment.
Have More Questions About Spray Foam R Values?
Natural Polymers offers top-of-the-line spray foam insulation, both open– and closed-cell. Natural Polymers is innovative, using chemistry and environmentally friendly raw materials to create sustainable products. Create your order now, or contact us today to speak with a spray foam insulation expert.