Facts About EPS and Water Absorption

By: Doug Wehrwein, Sales Representative

Extensive testing has confirmed that the closed-cell structure of EPS reduces moisture absorption over prolonged periods. Even when moisture absorption has reached the maximum threshold there is minimal effect on the thermal performance of EPS insulation. When you review the Expanded Polystyrene Industry Alliance Technical Bulletin 103 you’ll see that even when the moisture absorption level reached 4.8% the EPS insulation’s R value was still at 94% of what was expected. Conversely, the R-value of a comparable sample of XPS was only at 52% of what was expected and moisture level of the XPS sample was 18.9%.

The area in which water can migrate into in the EPS material is the tiny channels (or the interstitial space) between the fused beads of expanded polystyrene. These channels naturally exist in EPS rigid insulations boards and serve as the means to easily release the water when drying occurs. Moisture is present in the EPS long enough for adverse effects to take place. When XPS is exposed to bulk moisture repeatedly over long periods it may allow water in, where it them becomes trapped. See Expanded Polystyrene Industry Alliance Technical Bulletin 104 and 105. Generally, neither water nor water vapors affect the properties of EPS.

Foam-Control Plus+® Architectural EPS Insulation is a very cost-effective way to provide both superior thermal resistance and protection for underlying foundation moisture protection systems.

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