XPS vs. EPS rigid insulation: The difference is water absorption, says Owens Corning technical manager

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tyler simpson

Ottawa Construction News staff writer

Owens Corning Ontario technical manager Tyler Simpson has made the case for the advantages of extruded instead of expanded rigid polystyrene foam plastic insulation, proving that seemingly subtle differences in building products can have significant impact on the intended results.

Simpson provided members of Construction Specification Canada (CSC)’s Ottawa chapter data indicating that extruded (XPS) insulation “performs better than expanded (EPS) – and the source of the difference is in the manufacturing process.”

“XPS is manufactured in a continuous extrusion process that results in a homogeneous closed cell cross section,” Simpson told about 25 architects and engineers in the Ottawa Construction Association (OCA) boardroom on Jan. 21. “EPS is manufactured by expanding spherical beads in a mould, using heat and pressure to fuse the beads together where they touch, leaving open spaces between the beads where they don’t touch,” he said.

The difference – water can seep through the open spaces – dramatically reducing the insulation’s R-value when it comes into contact with water, with additional structural problems as the freeze-thaw cycle takes hold.

Simpson said: “There are a variety of tools and resources that have documented the effects water absorption has on the R-value of foam plastic insulation and which insulation best resists these adverse effects. As water is always present around structures it is critical products are selected that resist intrusion of water.”

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