Why is EPS a better choice for below-grade insulation?

By: Tom Huempfner, VP Sales & Marketing

Published vs. Long-Term R-value Performance

Did you know that not all rigid foam insulations Carver Hawkeye Arena Below-Grade EPS Insulationpublish their long term R-value? There are three commonly used sheet insulation materials. Extruded Polystyrene (XPS), Expanded Polystyrene (EPS) and Polyisocyanurate (ISO – a derivative of polyurethane). XPS and polyisocyanurate publish an inflated short term R-value. Only one of these materials has an R-value warranty for 100% of its published R-value. EPS publishes a slightly lower R-value per inch and per density than does XPS and Polyisocyanurate. However, the R-value EPS publishes is the long-term (warranted) R-value of the product. EPS does not off-gas or lose any of its thermal resistance over time.  See for yourself.  Read the R-value warranties for expanded polystyrene (EPS), extruded polystyrene (XPS) and Polyisocyanurate (ISO).

% of
20 Years
15 Years
10 Years

Water Absorption & R-Value

Did you know that when exposed to moisture EPS maintains a much higher % of its thermal resistance than does XPS or polysicocyanurate (a derivative of polyurethane)? A 15-year real world test compared the performance of EPS side-by-side with XPS. The test results showed that the higher the water resistance the more an insulation maintained its R-value.  More evidence of this can be found when holding an EPS foam cup, with a .06″ wall thickness, full of scalding hot coffee you can hardly feel the heat of the coffee. This demonstrates the thermal resistance of EPS when exposed to bulk moisture.

Compressive Resistance

Did you know you can purchase EPS with very high compressive resistance? You can purchase EPS sheet insulation at 10psi, 15psi, 25psi, 40psi and 60psi. The cost per sheet of EPS is less than the cost per sheet of XPS or polyisocyanurate at the same compressive strength. More importantly the cost per R-value and the long-term R-value of EPS are both significantly better than XPS and polyisocyanurate. EPS sheets also come in a variety of sizes:  in any thickness up to 36″ thick or 10′ long with no cost premium per board foot.

Saves Installation Labor and Money

EPS is a cost effective and dimensionally versatile sheet insulation. A contractor can save labor time and machine time if his perimeter insulation is cut to the height of the wall – whether its 40″ tall or 10′ tall. The cost for labor and machine time is a much bigger component to the overall budget than the insulation itself. The right insulation can help a contractor manage project costs.

Challenge yourself to learn more about EPS below-grade insulation!

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