Airpop® (EPS) Versus Extruded Polystyrene (XPS) - The Proven Differences

Last month we focused on building insulation materials and why Airpop® (EPS) outperforms XPS (Extruded Polystyrene).

This month, we want to share the similarities and differences between the two products Airpop® (EPS) and XPS insulation in a side-by-side comparison; based on field performance, below grade application and continuous 15-year installation period.

Airpop® Expanded Polystyrene (EPS):  foam is a closed-cell insulation that’s manufactured by “expanding” a polystyrene polymer; the appearance is typically a white foam plastic insulation material.

Extruded Polystyrene (XPS):  foam is a rigid insulation that’s also formed with polystyrene polymer, but manufactured using an extrusion process, and is often manufactured with a distinctive color to identify product brand.

Key Similarities:

  • Both are made with polystyrene resin
  • Both use trapped air as their long-term insulating medium
  • Both have a closed-cell structure
  • 50-year R-Value
  • Both fall under the same manufacturing standard: ASTM C578 Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. The ASTM C578 standard includes 14 different types of polystyrene. The different classifications relate directly to physical characteristics of each type—most notably, the density, compressive resistance, and R-value.

Key Differences:

  • Moisture resistance
  • R-Value
  • Environmental impact
  • Compressive strength

Moisture Resistance:

Airpop® (EPS): Real world study shows 15-years as a below-grade foundation insulation showed that EPS had retained 94% of its R-Value and only 4.8% moisture. The R-value at the time of excavation showed that EPS is less affected by moisture content than XPS.

XPS: The Same study shows 15-years as a below-grade foundation insulation.  XPS only retained 52% of its published R-value and contained a higher moisture content of 18.9%. The R-value at the time of excavation reflected that XPS is greatly affected by exposure to moisture.

Environmental Impact:

Airpop® (EPS): Contains up to 15% recycled content. Airpop® (EPS) has never contained HFCs, CFCs, HCFCs, formaldehyde or color dies. Natural color is white.

XPS: Has limited amounts of recycled content. XPS typically contains HFCs; they are harmful to the environment. XPS also contains dies like pink, blue or green are a few examples.

Image courtesy of the EPS-IA

Now, which foam would you choose? Case studies are located at  EPS – Industry Alliance.

Do you need further information for your next building project? Contact us at We’re happy to help.