Airpop®(EPS) vs. XPS: The R-Value Difference

Many technical differences distinguish  Airpop® (EPS, expanded polystyrene) and XPS  (extruded polystyrene) 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

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

During manufacturing, Airpop®’s (EPS) 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 one inch thick sheet with the same density allows for XPS to have a lower moisture absorption rating.

The Results

An article from the 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 Airpop® (EPS) and XPS, the results demonstrated that Airpop® (EPS) Insulation outperformed XPS insulation with better R-value retention and a lower moisture absorption.” Research also showed that the long-term application of XPS insulation results in a higher water retention and greater loss of R-value than reported when using standardized laboratory test methods.


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 (as seen below ).


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 the material used.


For moisture resistance, EPS absorbs small amounts of moisture quicker but releases it faster than XPS. Be sure to choose wisely.


Please click here for full research and results regarding EPS and XPS.