EPS vs. XPS: Proven Results For Better

Many technical differences distinguish EPS and XPS applications. One of the most prominent, that has been concluded through field and laboratory testing, is the diminished R-value in XPS inclusion after being exposed to high water absorption.


The Difference


EPS (expanded polystyrene) and XPS (extruded polystyrene) are both closed-cell rigid insulation made from the same base polystyrene resins. Although the same material they manufactured differently; EPS beads are molded or cut into various sizes and shapes while XPS is extruded sheets.  


During manufacturing, EPS’s blowing agent leaves the beads rather quickly creating thousands of tiny cells full of air. In contrast, XPS’s blowing agent stays embedded in the material for years, thus reducing the capability of air transfer through the material.  For this reason, a 1 inch thick sheet with the same density allows for XPS to have a lower moisture absorption rating.


The Results


An article from EPS-IA, XPS Insulation Extracted After Field Exposure Confirms High Water Absorption and Diminished R-Value, stated, “when water and R-value were compared between EPS and XPS, the results demonstrated that EPS Insulation outperformed XPS insulation with better R-value retention and a lower moisture absorption.”


The testing from standardized laboratory or in the field results demonstrated no correlation between exposure for XPS water absorption. However, the significant loss of R-value  associated with XPS water absorption are shown. (see graph )

Why Choose EPS


Studies show that as much as 25% of energy loss from a structure can be attributed to a lack  of insulation. When insulating below grade, it is important to analyze and know the moisture resistance and thermal performance (R-Value) prior to making a decision on material used.


For moisture resistance, EPS absorbs small amounts of moisture quicker but releases it faster than XPS…choose wisely. Please click here for full research and results regarding EPS and XPS.


For your EPS below grade insulation needs, please contact sales@plymouthfoam.com.