EPS insulation: what it is and how it behaves
Expanded polystyrene is a rigid closed-cell foam that is about 98 percent air. It has no blowing agent to lose, no food value for mould, and enough compressive strength to act as a structural web.
How it is made and what that means
Polystyrene beads are expanded with steam and fused in a mould. The result is mostly air held in a cell structure, which is why it insulates and why it is light.
Unlike some foams, EPS is blown with air rather than a hydrofluorocarbon. It has no blowing agent to diffuse out over time, so it does not show the thermal drift that some products do.
Structural, not just thermal
EPS has real compressive and flexural strength, tested under ASTM D1621 and C203. That is what allows it to serve as the web of a panel rather than as loose fill, and what stops interior and exterior finishes from buckling.
Density is the property that drives both strength and R-value, which is why a specification names a density and a type under ASTM C578 rather than just saying foam.
The environmental argument
All insulation has an environmental footprint, and cement, rockwool and fibreglass are all carbon-intensive to produce. EPS is unusual in how little material is in it relative to the volume it fills.
What Guardian publishes
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The Shield™ core is UL certified modified expanded polystyrene, minimum density 0.90 pcf, Type I, complying with ASTM C578.
Source · 3-Part Specification 1.5 E.5 a
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Guardian states EPS is 98 percent air, can return up to 200 times the energy required to produce it, reduces emissions by up to 100 times the volume produced in manufacture, is non-toxic and inert, and contains no CFCs or HCFCs at any point in its life cycle.
Source · Products page, environment section
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Guardian states there is no degradation of the EPS insulative qualities over time.
Source · Differentiation sheet
Go deeper
Standard Test Methods for Breaking Load and Flexural Properties of Block-Type Thermal Insulation
ASTM C303Standard Test Method for Dimensions and Density of Preformed Block and Board-Type Thermal Insulation
ASTM C578Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation
ASTM D1621Standard Test Method for Compressive Properties of Rigid Cellular Plastics
Panel typeWall panels
FAQDoes the insulation degrade over time?
FAQWhat is the environmental case for EPS?
Written by Data Subsystems, for Guardian Structural Technologies. Last updated .
Drafted from Guardian Structural product literature and published building-science sources. Awaiting Guardian technical review. Confirm any figure against the current product documents or ask us before you rely on it in a design.