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 absorbs and retains less moisture than EPS - below grade
Field study says - Not true
Compare Water Absorption by % XPS VS EPS
Published Water Absorption by Total Immersion
Field Study R-Value Per Inch*
“Having accurate data is a key ingredient in choosing the proper insulation for your foundation wall because it not only effects the entire energy efficiency of the building but also the dryness. “
Real Science
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EPS Stands Out

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Real science conducted in real world application provide quite a difference. These results suggest very clearly that short term laboratory tests of water absorption for XPS does not necessarily reflect the long term below grade performance of these materials.
Additional Interest Facts About Water Retention
EPS Dries Out
One of the great properties of EPS is that water that is absorb can expel out. EPS insulation exhibited drying potential under severe exposure conditions while XPS, when exposed to the same conditions, did not. Read More
EPS Hold R-Value Even When Wet
EPS foam will maintain its R-value, even with significant saturation percentages. In contrast, Extruded Polystyrene (XPS) foam is more dramatically affected by small amounts of moisture. Read More
Freeze-Thaw No Loss R-Value or Strength
These independent tests confirm the freeze‐thaw and moisture resistance properties of EPS insulation. Test results confirm no loss in R‐value or change in compressive strength for EPS. Read More
The long‐term application of XPS insulation below grade results in a higher water retention and greater loss of R‐value than reported when using standardized laboratory test methods. Water absorption results for XPS using ASTM C272 cannot be correlated to the in‐service performance of extruded polystyrene foam insulation.
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