Comparing EPS and XPS Insulation

The test of below grade insulation, conducted by AFM Corporation in cooperation with the Expanded Polystyrene Molders Association, determined the R-value and water absorption of an EPS and an XPS product.

The test of below grade insulation, conducted by AFM Corporation in cooperation with the Expanded Polystyrene Molders Association, determined the R-value and water absorption of an EPS and an XPS product.

This microscopic photo of an EPS resin bead shows that EPS has a closed-cell structure, dispelling one industry misconception. The honeycomb cell structure is what gives EPS its high compressive strength. EPS doesn’t absorb water into its closed cells.

Samples of EPS and XPS insulation were placed into service in 1993 and had 15 years of use as vertical wall insulation separating the heated building foundation from soil on the exterior foundation of a building in St. Paul, MN. Samples were removed in the summer of 2008, brushed clean and tested immediately upon excavation for R-value. EPS and XPS samples were immediately adjacent to each other and were both on the foundation for 15 years. At the time of excavation the soil in contact with the insulation was dry and no abnormal conditions were observed. Both sets of samples were subsequently conditioned in a laboratory (72° F, 50% RH) for four weeks to determine a conditioned R-value. In addition, the moisture content of the samples was also measured.

Samples of EPS and XPS insulation were placed into service in 1993 and had 15 years of use as vertical wall insulation separating the heated building foundation from soil on the exterior foundation of a building in St. Paul, MN. Samples were removed in the summer of 2008, brushed clean and tested immediately upon excavation for R-value. EPS and XPS samples were immediately adjacent to each other and were both on the foundation for 15 years. At the time of excavation the soil in contact with the insulation was dry and no abnormal conditions were observed. Both sets of samples were subsequently conditioned in a laboratory (72° F, 50% RH) for four weeks to determine a conditioned R-value. In addition, the moisture content of the samples was also measured.

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