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There is a long-standing debate over whether expanded polystyrene (EPS) insulation or polyurethane (PUR) insulation is a better material to use for insulation. This is a complex debate that requires knowledge about several different factors. So, let’s start at the beginning.
Expanded Polystyrene (EPS) Insulation is a rigid closed cell plastic foam that is comprised of hollow, spherical beads that are fused together using steam. Because EPS insulation is 98% air, it is chemically inert. [i] [ii]
Polyurethane Insulation is “… a foam insulation material that contains a low-conductivity gas in its cells.” [iii] It is “… formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives.” [iv]
Structural insulated panels (SIPs) are manufactured using both types of insulating materials. So how do they compare?
Polyurethane insulation has one of the highest initial (at the time of installation) R-values per inch in the industry; higher than EPS insulation in equivalent thicknesses. However, unlike polyurethane, EPS insulation will maintain its initial R-value long after it is first installed.
Polyurethane insulation uses the thermal resistance of its blowing agent to attain higher initial R-values. However, polyurethane insulation loses R-value over time due to thermal drift. According to the Building Science Corporation, thermal drift is, “[t]he loss of R-value over time in foam insulation that contains captive blowing agents. Air enters the cells of the foam, diluting or replacing the lower-conductivity blowing agent…”
According to the US Department of Energy, most thermal drift of polyurethane insulation occurs during the first two years. Oak Ridge National Laboratory chose to study the effect of thermal drift on “aged” R-value, or long-term thermal resistance (LTTR), after a five-year period. They found that in as short as 2-5 years, the thermal resistance of EPS insulation and polyurethane insulation will be nearly equivalent.
Polyurethane insulation is more expensive than EPS insulation. This cost is due to an initial higher R-value. However, as the Oak Ridge National Laboratory study shows, this R-value degrades over time due to thermal drift. And, at the end of five years, the long term thermal resistance is similar. At the end of the day, you need to ask yourself why you should pay a premium for a product that will lose its primary advantage after five years.
The Insulspan SIP System has been independently tested and received a one-hour fire-resistance rating, see Technical Bulletin 108. Although EPS insulation is considered combustible, this does not mean that it will burst into flame. It simply means that it behaves similar to other materials such as wood or paper. Fire codes usually require a fire barrier on the interior face of any wall (no matter the insulation type), which is easily met by using a gypsum wallboard.
There are few things to consider when moisture is mentioned, including absorption, disbursement, and mold growth.
The EPS Industry Alliance commissioned Intertek Testing Services NA Ltd., an independent test laboratory, to conduct tests on several types of polystyrene foam. Their results “. . . have shown that EPS insulation installed in well-constructed roofs does not absorb appreciable moisture, well under conditions characteristic of prolonged, cold, damp winters. The same amount of moisture absorbed (an average of 0.2% by weight) has little or no effect on its compressive or flexural strength, and the EPS insulation retains between 95% and 97% of its thermal efficiency.”
Polyurethane insulation also has a low moisture permeability.
Because both polyurethane insulation and EPS insulation are closed cell structures that resist moisture absorption, both products are equally capable of resisting mold growth.
Now that you have a better understanding of the differences between EPS insulation and polyurethane insulation, Contact Us today to start your new home project or ask additional questions.
[i] “Expanded Polystyrene (EPS): A lightweight closed-cell insulation with endless applications,” Insulation Corporation of America, https://insulationcorp.com/eps/
[ii] “Properties of EPS,” Expanded Polystyrene Australia, http://epsa.org.au/about-eps/what-is-eps/properties-of-eps/
[iii] “Insulation Materials: Polyurethane Insulation Materials,” Energy Saver, An Office of U.S. Department of Energy, https://www.energy.gov/energysaver/weatherize/insulation/insulation-materials#polyurethane
[iv] “Introduction to Polyurethanes: How Polyurethane is Made,” American Chemistry Council, https://polyurethane.americanchemistry.com/How-Polyurethane-is-Made/
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