The EPS vs XPS Moisture Resistance & Permeability Conversation

By: Pat Austin, Sales Representative

Hey John, when you’re right, you ARE right! To expand a little on your below-grade insulation performance conversation, I’d like to add a couple points.

First, the ASTM C272 quality control testing for extruded polystyrene is in my opinion the reason that most below-grade insulation is either pink or blue (those are the dyes the XPS manufacturers brand their products with).  But as you stated, this has no correlation with actual in-service performance.  In fact, several independent laboratories have published reports showing EPS to perform better in both real world and laboratory tests.

Test Reports:

So as you accurately pointed out, ASTM C272 quality control moisture testing severely misrepresents actual in-service performance.  Foam-Control® PLUS+® insulation outperforms XPS because its permeability allows it to dry out.

But John, it even gets better!  Research conducted by BASF back in the early 1990’s proved that XPS loses R-value over 10X faster than EPS when exposed to moisture gain.  In BASF’s own words, “EPS is far more resistant to adverse thermal impacts than many other insulations, including as an example extruded polystyrene.  See Table III.”

BASF E2 Front Page

As you so accurately stated, Foam-Control® PLUS+® is the superior rigid foam insulation, especially when handling exposure to bulk moisture.

About Pat Austin

BSIE from Marquette University in 1986, MSMSE from UW Madison in 1989. General contractor for 13 years before joining the ACH Foam team in 2007. Married to Kelly, with four sons.
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