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XPSA > Benefits > Moisture Resistance

Moisture Resistance

When moisture gets into a wall assembly, it can reduce the overall R-value of the building envelope. But properly installed XPS sheathing provides a continuous layer of protection against inside and outside moisture.

XPS is manufactured in a proprietary process that melts plastic resins and additives into a molten material which is then extruded through a die, where it expands and cools into a uniform closed-cell rigid foam insulation board. This uniform closed-cell structure is inherently moisture resistant.

Per ASTM C 578, without the need for a facer or laminate, XPS products only absorb 0.3 percent water by weight. (This compares to molded, expanded polystyrene foam products, or EPS, whose same property ranges from 2 to 4 percent, depending on the density of the product.) In addition to its closed-cell structure, XPS foam products have a natural “skin” surface which is not conducive to moisture absorbency, including in below-grade applications.

XPSA Headquarters

529 14th Street, N.W.
Suite 1280
Washington, DC 20045

Phone Number:
202.207.1113

About XPSA

The Extruded Polystyrene Foam Association (XPSA) is a trade association representing manufacturers of Extruded Polystyrene Foam (XPS) insulation products and the industry’s raw material suppliers. XPSA members collectively manufacture more than 95% of all XPS destined for use in the North American market. XPSA promotes the benefits that accrue to society from appropriate use of XPS foam insulation applications.

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