Busting The Insulation Myths
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For years we have been told that XPS (Extruded Polystyrene) insulation is better than EPS (Expanded Polystyrene) for below grade insulation.

Is this true?
What about the new research?

Myth: XPS has a higher R-Value than EPS - below grade
Not Exactly True
Compare 25 PSI (250) Product R-Value
XPS 250
EPS 250
Published R-Value Per Inch*
Guaranteed R-Value Per Inch*
Field Study R-Value Per Inch*
Real World Results Matter
  • Field studies mirror real world resultsFor years XPS foam was the choice and recommendation for below grade insulation, but after a 15 year study was conducted by an independent Test Lab. (In-Situ) EPS foam significantly outperformed XPS foam not only in its retention of its R-value but also showed superior properties in decreased water absorption.
  • Published R-Value reflect perfect laboratory conditions As a starting point, published ASTM results is important for product comparison. Unfortunately, these results are under perfect lab conditions and not real world conditions. Real world variables are numerous, however independent research over long periods in real conditions should be highly favored in design considerations.
  • Performance is what you pay for. The dramatic difference in long-term insulation performance is so significant that Architects, Engineers, Contractors, Builders, Building Inspectors and Home Owners should be aware of these test results and true facts when determining which insulation would offer the most long term insulation value and energy savings. EPS continues to be the best insulation value. EPS Cost/R-Value inch vs XPS can be as much as 50% better considering field studies. This only the initial cost of material and not even taking into account long-term operational performance costs.
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* Published R-Values come directly from the manufacturer’s publications. XPS R-values were used from Owens Corning and Dow. Guaranteed R-value was from XPS Manufactures publication - See Warranties. Field Study R-values where extrapolated from In-Suit Research and for comparative analysis purposes only.
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