Closed Cell VS. Open Cell Foam Insulation
What’s the difference between open cell & closed cell? Others will say there’s no big difference. Some will tell you it’s all about price per square foot. And, some just don’t know what they’re talking about.
You want the facts necessary to make an educated decision … We’ve got your answers here.
Polyurethane spray foam is often categorized as either “open cell” or “closed cell”. There are several major differences between the two types, leading to advantages and disadvantages for both, depending on the desired application requirements. In addition, polyurethane spray foam is an extremely versatile material that is available in a variety of final physical properties and densities, making it necessary for the end-user to have an understanding of these differences in order to choose the spray foam system that is best suited for the particular application requirements, meets code, and follows Best Building Practices.
Closed Cell Spray Foam
EnviroGreen’s closed cell spray foam is among the most efficient insulating materials for residential and commercial applications, with an R-value of 6.8 per inch. Common foam density for closed-cell polyurethane foam is approximately 1.7 to 2.0 pounds per cubic feet. This foam expands roughly 30 times its initial liquid size, and rarely requires trimming which results in little to no waste.
EnviroGreen’s closed-cell polyurethane foams are characterized by their rigidity and strength, in addition to the superior R-Value. These heavier and denser foams have what is known as a closed-cell structure, which means that the gas (EPA approved Honeywell 245fa) bubbles that form during the application process remain permanently locked into the cured foam. These millions of microscopic bubbles created during the manufacturing stage remain closed and intact, thus trapping the reaction gases. Therefore the R-Value of EnviroGreen’s closed cell foam is close to that of the reaction gas, or 6.8 per inch. Since there are no open interconnections between individual bubbles, the foam can not absorb water and also effectively diffuses (retards) the passage of water vapor.
According to most building codes, a vapor retarder must have a perm rating of less than 1.0; EnviroGreen’s closed-cell foam exceeds this standard. And, very importantly, due to the closed-cell structure and higher density range, it provides the optimum strength increasing shear and racking stability by up to 300%. Due to its water barrier qualities and this increased strength the federal government currently offers a Residential Property Storm Mitigation Incentive tax credit of 50% of the cost of the material and installation up to $5,000 when properly installed under the roof-decking.
One additional note concerning closed cell foam is that some companies market and install closed cell foams without this 245fa (or comparable inert gas) blowing agent. These products begin to lose some of the benefits that are characteristic of true closed-cell polyurethane foams.
Without this blowing agent the foam may suffer a significant amount of vapor diffusion and/or vapor barrier qualities and should therefore create concern when being used for these reasons, such as under floors or in the exterior walls of old wood-sided homes without code approved vapor retarders for example.
Open Cell Spray Foam
EnviroGreen open cell spray foam is also referred to as ½ pound or low density foam. This foam expands to over 100 times its initial liquid size and may require trimming and disposal of the excess waste material after application. The physical characteristics of EnviroGreen’s open-cell polyurethane foam usually include a softer “spongier” appearance, as well as lower strength and rigidity than closed-cell foams.
Open cell foam cures soft while the irregular bubbles which form during the expansion-reaction process remain open and interconnected. EnviroGreen open cell foam derives its R value of 3.8 per inch from the dormant air within the open bubble pockets which is about half that of closed-cell foam. The R-Value of open cell foam is quoted close to that of conventional fiberglass and cellulose insulation based on the same principle of trapping dormant air. These similarly quoted insulation R-values are very misleading since open cell foam is an air barrier and may significantly slow moisture transfer relative to these competing insulations. Under real life conditions open cell foam performs at its stated R-value whereas the R-value of fiberglass and cellulose degrade do to air flow (convection) through and within the material, commonly poor installation practices, and extreme temperature differences.
Please view “The R Fairy Tale” and “Oak Ridge Labratory’s” study on fiberglass insulation for more information about the inaccuracies of R-values. Open cell foam significantly slows down convection through and within the wall cavity. Open cell spray foam, however, is more permeable to water vapor than closed-cell, with perm ratings of approximately 16 per 3 inches thickness, and therefore is not a code approved vapor barrier/retarder. Open cell foam should not be used in exterior applications, such as underneath a raised house, due to its inability to retard moisture flow. However, EnviroGreen open cell foams are incredibly effective as a sound barrier, having about twice the sound resistance in normal frequency ranges as closed-cell foam.
Applications that typically use open cell foam include residential construction insulation, under roof trusses for “conditioned attics”, and for sound deadening in media rooms, etc. Closed-cell foam, while a superior insulating product used in residential construction, is also used in a variety of commercial and industrial applications because of the excellent strength and insulating properties and vapor barrier qualities which may be required by building codes.
Hybrid 1.0lb to 1.2lb Open Cell Spray Foam
EnviroGreen also offers a spray polyurethane foam that includes characteristics of both closed-cell and open cell products. This insulation is referred to as a “hybrid” or sometimes “double density” polyurethane foam.
This unique insulating product is more characteristic of an open cell material and by definition is an open cell product since it does not contain a blowing agent such as Honeywell 245fa which historically was required to be defined as a true closed cell foam. It is characterized by its more rigid feel and additional strength relative to typical ½ pound open cell products, although it does not provide nearly as much rigidity and strength as closed cell foam and should not be used in place of closed-cell for these reasons. The R-value is 5 per inch due to the additional “insulating material” instilled during the manufacturing process. Whereas open cell spray foam contains a half pound of insulating material per cubic foot, and closed-cell foam contains 1.7lbs to 2.0lbs per cubic foot, EnviroGreen’s hybrid foam contains 1.2 pounds of insulating material per cubic foot. This 1.2lb open cell foam exhibits similarly excellent air-barrier characteristics of closed cell insulation but less ability to retard the flow of moisture.
Although EnviroGreen strongly encourages the use of only 245fa closed cell foam for exterior applications such as under the framed floor of a raised house this 1.2lb product may be installed under a very narrow set of circumstances in similar cases.
Beware!!! Many foam companies install 1.2lb foam in place of a closed cell insulation that may have been quoted in an estimate or contract. It may be very difficult to detect the differences between these two products after installation. It has been our observation that there have been many cases where companies quoted closed cell foam but fraudulently installed 1.2lb instead without the knowledge of the homeowner.