Expanded polystyrene (EPS) and eXtruded polystyrene (XPS) are both closed-cell foams and similar in appearance but the manufacturing process, a key ingredient, and resulting material properties and emissions are very different.
|Impact Category||Units||XPS Total||EPS Total||EPS is better by|
|Ozone Depletion||kg CFC-11 eq||3.63E-4||1.6E-8||2,268,650%|
|Global Warming||kg CO2 eq||60.8||2.79||2,079%|
|Acidification||mol H+ eq||1.78||0.46||287%|
|Eutrophication||kg N eq||9.85E-4||3.6E-4||174%|
|Total Solid Waste||kg||0.857||0.75||14%|
|Smog Formation||kg O3 eq||0.208||0.20||4%|
The Functional Unit is 1 m² [10.764 ft²] of rigid cellular polystyrene (RCPS) insulation board with a thickness providing an average thermal resistance of RSI = 1 m²·K/W [imperial R-Value = 5.68 hr·ft²·°F/BTU] and with a building service life of 60 years.
We all know XPS from its use in commercial buildings supplied by large corporations in mostly blue, pink, and yellow boards. And many of us remember XPS for its use in fast-food packaging with extremely ozone-layer depleting CFC Gases before the worldwide ban starting in the 1990s. Currently XPS and most polyurethane (PU) sprayfoam insulation use HCFC Gases which the whole world also agreed to ban due to high GWP. The HCFC Gases escape from XPS at a pretty slow rate.
In contrast, EPS uses pentanes as the blowing agent which get replaced by 100% Air within the first few months after manufacture. EPS is usually white or gray.
XPS manufacturers use a specific HCFC Gas with lower thermal conductivity than air, allowing them to claim higher R-Values per inch thickness than EPS. However, that's only because the applicable laboratory tests are relatively short-term at a few days, 180 days or 5 years. After 10-15 years the reality is very different for the remainder of a building's long life-cyle: after the Gases escaped from XPS, it should have the same R-Value per inch thickness as EPS. But many real-life installations of XPS exhibited much lower R-Values than expected.
So the EPS Industry Alliance commissioned additional tests of long-term field performance and released a Technical Bulletin about Polystyrene Foam's Water Absorption & R-Values.