Is Graphite Polystyrene (GPS) An Open Or Closed Cell Insulation? (And Why It Matters!)

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Is Graphite Polystyrene (GPS) An Open Or Closed Cell Insulation? (And Why It Matters!)

Insulation can be referred to as either open or closed cell insulation.  Cell structures of closed-cell insulation are completely closed.  Whereas open-cell insulation is made up of cells that aren’t completely closed – cell walls are open or shared.

Both insulation types are generally used for specific purposes.  Spray foam insulation is available as an open-cell (in addition to a closed-cell) useful for sound attenuation and filling hard-to-reach areas.  Rigid insulation such as XPS, EPS and GPS are closed-cell insulation products, which are denser and offer higher R-values than open cell insulation.

Neopor Beads

Unlike XPS insulation, EPS and GPS insulation are manufactured using a molding process.  When heat or steam is applied the beads expand and fuse together taking the shape of the mold.  This process creates a closed-cell structure with voids between the expanded beads – the voids do not define EPS as open-cell insulation1.   The voids make these insulation products more permeable than XPS, which is beneficial when used as exterior insulation – provides better drying capacity for exterior walls.  And based on independent studies EPS and GPS show it retains a much higher long-term R-value in wet conditions compared to XPS. 

  1. The Canadian and US standards for testing rigid insulation both define EPS as a closed-cell insulation – CAN/ULC S701, “Standard for Thermal Insulation, Polystyrene, Boards and Pipe Covering,” ASTM C578, “Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation.”

About the author:
Andy Lennox
President, Logix Brands Ltd.