EPS vs. XPS: You Be The Judge

Technology is constantly developing; there are breakthroughs and there are challenges. Therefore, it’s important that we update you now on the latest news from the EPS Industry Alliance (EPS-IA).


Earlier this year, EPS-IA issued two new documents regarding moisture absorption. As we said earlier, there are challenges in any field.  You guessed it: A challenger has stepped up to debate the durability of EPS. Not only that, but they have also claimed that extruded polystyrene (XPS) is the better option.


So let’s try to understand the debate, beginning with the basics. EPS (expanded) and XPS (extruded) are both closed-cell rigid insulation made from the same base polystyrene resins and manufactured differently, EPS is beads that 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 while XPS’s blowing agent stays embedded in the material for years, thus reducing the capability of air transfer through the material.  For the same 1 inch thick sheet with the same density, XPS has a lower moisture absorption rating than EPS due to these differences.


When it comes to water, you have two variables; absorption and retention.  Moisture intrusion into building materials is sometimes unavoidable. It is important to evaluate material performance when exposed to long term environmental conditions. Insulation materials need to resist moisture intrusion, but just as importantly be able to exhibit drying potential to maintain long term thermal integrity.


Here is where EPS outperforms XPS for long term R-Value (keeping your home or building climate controlled).  When exposed to the extreme conditions of the ASTM C1512 test (Standard Test Method for Characterizing the Effect of Exposure to Environmental Cycling on Thermal Performance of Insulation Products), EPS insulation exhibited drying potential for under severe exposure conditions while extruded polystyrene did not exhibit drying potential when exposed to the same conditions. The drying potential for thermal insulation is critical to maintaining thermal resistance (R-value) under severe long term exposure conditions.


There are plenty of other technical differences between the two, so the debate will be a detailed one as research continues. Plymouth Foam remains proud to manufacture and sell EPS products in addition to supporting the EPS Industry’s findings with the assistance of third party researchers. Please view these findings: http://www.epsindustry.org/building-construction/moisture-resistance.