When making a decision between EPS and XPS and you prefer the option with the higher R-Value, then EPS is the answer.
In recent years, studies continue to show how EPS outperforms XPS on R-Value. Below are the results of three research studies performed by the EPS Industry Alliance on the R-Value of EPS vs XPS. On their website you can find a wealth of information and research to support EPS and its application as a building material.
EPS R-Value Retention & Water Absorption
The EPS Industry Alliance completed an impressive 15-year in-situ research study on the comparison of EPS vs XPS R-value in below grade installation when placed side by side. They unearthed the findings and EPS has come out on top, again. The water retention of EPS was significantly less than XPS as stated in the graph below.
In-Situ R-Value Retention and Water Absorbtion
EPS R-Value Thermal Performance
The EPS Industry Alliance completed a 30-month exposure study on Thermal Performance. Here is an excerpt from the study’s highlights:
Testing confirmed that all types of EPS insulation retained their specified thermal and mechanical properties even after being subjected to in-situ freeze-thaw cycling.
- The moisture content of EPS insulation directly exposed to high moisture content soil conditions was found to be less than 0.5% by volume on average at the end of the exposure.
- In-situ thermal performance of the EPS insulation monitored during the exposure period remained constant, i.e., there was no loss in thermal resistance.
- Laboratory test results from samples removed after the exposure confirmed thermal performance and durability, i.e., there was no change in material properties.
EPS Mold Resistance Properties
Most building materials require special surface treatment to protect from mold growth, while EPS is often installed untreated because of its natural mold resistant properties. The Technical Bulletin published by The EPS Industry Alliance states:
Expanded polystyrene (EPS) rigid foam insulation was tested in accordance with ASTM C1338 “Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings” which is used to evaluate the ability of new insulation materials to support five types of fungal growth. Third-party testing conducted by SGS US Testing Company, Inc. demonstrates that under laboratory controlled conditions favorable for the growth of mold that EPS scored no traces of growth over a 28-day incubation period.
Value of EPS as an Ideal Below Grade Building Material
Not only does EPS hold its R-Value over time but it is also mold resistant making it an ideal material to install in below grade construction where conditions are optimal for mold growth, such as basements in a residential home.
EPS performs in the following areas: stable thermal R-value, minimal moisture absorption and resistance to mold. Which makes it an obvious choice for a building construction material. Contact an Alleguard sales representative to learn the cost savings behind switching from XPS to EPS for your next below grade project.