Spray foam insulation is one of the most effective ways to protect your attic against unwanted energy loss. Unlike other forms of insulation that must lay on the floor of the attic, spray foam can be applied directly to the underside of your roof. There, it provides unparalleled insulating ability, while also forming an effective barrier against air leaks.
The benefits of spray foam make it a great choice for virtually any residential application. Yet first you must decide between the two main types of spray foam: open-cell and closed-cell. This article will help to prepare you for this key decision by outlining four must-know differences between open- and closed-cell spray foam insulation.
Open-cell and closed-cell spray foams differ greatly in terms of their density once they have fully cured. Simply put, open-cell varieties have a much lower density — about 0.5 pounds per cubic foot. Closed-cell spray foam, on the other hand, tends to have a density of approximately 2 pounds per cubic foot.
The low density nature of open-cell spray foam means that less material is required in order to insulate a given area. Because fewer resources are required, open-cell foams often cost significantly less than their closed-cell counterparts. Yet the density of closed-cell spray foam gives it a much greater insulating power.
Manufacturers express the power of any form of insulation using the metric known as R-value. The greater an insulation's R-value, the better its ability to prevent energy loss. Because of its higher density, closed-cell spray foam has almost double the R-value of open-cell spray foam. Closed-cell varieties have an R-value of around 6.5, while open-cell varieties have an R-value of between 3.5 and 3.6.
For those living in especially cold climates where a higher R-value is needed, the cost difference between open-cell and closed-cell spray foam won't be quite as pronounced. The higher R-value of closed-cell spray foam means that less of it will be required in order to insulate an attic to a predetermined level. Open-cell foam, on the other hand, would need to be installed to a much greater depth to achieve the same results, making it cost about the same at the end of the day.
3. Vapor Barrier
The two varieties of spray foam differ greatly in terms of their ability to prevent moisture from passing through. As its name would imply, open-cell spray foam cannot stop moisture penetration. Closed-cell spray foam, on the other hand, forms an impenetrable vapor barrier. This ensures that mold and other moisture-loving microorganisms cannot take up residence in your attic.
In order to prevent water vapor from passing through, those who opt for open-cell spray foam must install some form of vapor barrier before applying the insulation. This may take the form of a vapor-retarding sealant painted onto the inner surface. It may also take the from of a sheet of thin plastic attached to the roof sheathing before spraying the foam into place.
4. Blowing Agents
All spray foams use what is known as an insulating gas, or blowing agent. This gas helps to form the foam's structure. In the case of closed-cell spray foam, much of the blowing agent remains trapped in the cells. There, it boosts the insulating power of the foam. Open-cell foams, on the other hand, lose a lot of their blowing agent due to their open nature.
Most open-cell spray foams use either water or carbon dioxide as a blowing agent. Closed-cell foams, on the other hand, often use hydrofluorocarbons and other chemicals linked to global warming. For this reason, closed-cell spray foams have come under increased scrutiny in recent years, with manufacturers working to implement safer blowing agents.
Choosing between open-cell and closed-cell insulation can be daunting. But with the help of a professional insulation company, you can determine the best fit for your home. For more information, please contact our spray foam pros at Spray Foam Tech, LLC.