Busting The Insulation Myths
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For years we have been told that XPS (Extruded Polystyrene) insulation is better than EPS (Expanded Polystyrene) for below grade insulation.

Is this true?
What about the new research?

Myth: EPS is not as strong
False - EPS has many various densities up to 8,640 PSF. In Fact, EPS And XPS Insulation use the same measuring stick for strength - ASTM D1621.
EPS mechanical strength varies with its selected density or type. One way to determine the strength of EPS is by measuring its “Compressive Resistance” or capability for materials to withstand loads. EPS having resistance to compressive stress is one the most important property of a building products. In fact, Plymouth Foam’s EPS compressive resistance can vary from 1,440 - 8,640 psf at 10% strain deformation (ASTM D 1621). Design considerations should be made as to which EPS type is needed or required.
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Flexural Strength is another measurement used to determine how “durable or brittle” a product performance might be. Flexural strength is really determining its “bending strength.” EPS insulation is used in most application as a filler not a pure structural product but it is good to know the flexural strength of a product.
Note: Exposure of EPS to moisture resulting from such factors as periodic, internal condensation or moist soil conditions in foundation applications do not affect the mechanical strength characteristics of EPS thermal insulation board. 
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