Building Insulation Products Geostructural Foam

Elastic Inclusion

The geosynthetic Elastic Inclusion EPS produced by Cellofoam North America Inc. is composed of expanded polystyrene that is molded, aged, and pre-stressed for construction projects that require an energy absorbing capability to handle dynamic loads. This compressible inclusion uses a modified bead containing a fire retardant and an insecticide to provide resistance against termites and other insects. Cellofoam Elastic Inclusion EPS has been strained beyond the yield point and then unloaded to elasticize the EPS product. The subsequent material exhibits linear-elastic behavior up to approximately 10 percent strain and linear proportional stress-strain behavior up to about 30 percent strain. As a result of Cellofoam’s manufacturing process, and confirmed by extensive independent and in-house laboratory physical property testing, Cellofoam Elastic Inclusion has a compressive strength tolerance of 720 psf ± 60 psf at 10% strain in the prestressed direction.

Testing equipment in Cellofoam's laboratory - close-up of compression testing using ASTM D1621 Standard Test Method for Compressive Properties of Rigid Cellular Plastics
Testing equipment in Cellofoam's laboratory
Stress Strain Diagram for EPS Elastic Inclusion vs Geofoam
Table of EPS Elastic Inclusion Specifications


The figure above depicts typical stress-strain relationships of plain EPS versus Cellofoam Elastic Inclusion EPS. The test data was acquired via compression along the elasticized axis at a rapid loading strain rate of 10% per minute at room temperature, using conventional EPS compressive test methods. A comparison of the typical stress-strain curves of the standard 1.0 pcf and 1.25 pcf EPS contrasts sharply with that of the Elastic Inclusion EPS. The latter is more linear and illustrates a significantly lower compressive strength in the prestressed direction.


Cellofoam’s Elastic Inclusion EPS is manufactured to provide very different characteristics and physical properties than our other EPS types. Cellofoam EPS used for insulation, EIFS, and Geofoam, for example, follow ASTM C578, ASTM E2430, and ASTM D6817 specifications, respectively. These EPS materials exhibit a linear-elastic stress-strain relationship at relatively low deformations or strains, usually up to only around one or two percent. Since the elastic region generally provides acceptable short-term deformation to loads as well as limits long-term creep to reasonable values, the standard design limit for most structural EPS (such as Geofoam) is usually at around one percent strain. At much higher strains, normal EPS no longer exhibits elastic behavior. Instead, it experiences unpredictable permanent plastic deformation, and thus does not return to its original shape once the load is removed.

There are applications, however, where structural EPS with a broader elastic range is needed, especially to act as an energy absorbing buffer between structures and dynamic surcharge loads such as those imparted by traffic or ground movements from earthquakes. In these cases, much larger strains than one percent might be experienced, sometimes repeatedly. With its linear-elastic stress-strain behavior up to approximately 10 percent strain, and predictable and tight constraints on compressive resistance, Cellofoam’s Elastic Inclusion EPS is an excellent solution to many compressible inclusion design needs. The following table provides a summary of Elastic Inclusion physical property specifications.


Due to its unique energy absorbing property, Elastic Inclusions are commonly used on bridges or other building structures to reduce the effects of the dynamic loads applied, such as traffic surcharge, or the temporary increase in earth pressures during construction or seismic events. Cellofoam Elastic Inclusion EPS provides the design engineer with consistent and predictable anisotropic stress-strain behavior, making this product ideal for protective applications for culverts and buried pipes, tunnels, bermed structures, retaining walls, and bridge abutments. In particular, Cellofoam Elastic Inclusion EPS is well-suited for use on bridge backwalls and wingwalls where large earth pressures and excessive settlement of approach embankments from cyclical, thermal expansions of the superstructure are a concern. In many cases, Elastic Inclusions have served to lower net construction costs by reducing the amount of more expensive materials used, such as concrete and steel.

An example of Cellofoam Elastic Inclusion EPS in use is shown by the photo at the top of this webpage. Working with Universal Foam Products in the fall of 2019, Cellofoam Elastic Inclusion EPS was incorporated into an I-95 overpass bridge construction project in Harford County, Maryland (photo courtesy Universal Foam Products,

While Cellofoam Elastic Inclusion EPS is usually used in new construction, it may also be employed to cost effectively rehabilitate or retrofit existing structures to increase design life or design safety factor for geotechnical or structural loads from seismic activity, expansive soils and rock, or even nearby traffic loads from roadways, trains, or airports. Rehabilitation is a very important application of Elastic Inclusion as in many cases it can improve public safety at dramatically reduced costs compared to tearing down and rebuilding structures.

Advantages of Cellofoam Elastic Inclusion EPS

Cellofoam Elastic Inclusion material has numerous advantages over other materials that have been employed in compressible inclusion applications, such as bales of straw, wood chips, or cardboard as these materials decompose over time and consequently have changing and unpredictable mechanical properties.

Additionally, Cellofoam Elastic Inclusion EPS is anisotropic with respect to compressive strength, which is significantly higher in the axis perpendicular to the prestressed direction than it is in the prestressed direction. This allows for some advantageous design applications such as use of this product to absorb energy and compress in one direction while providing stiffer compressive strength to support greater loads in another direction perpendicular to the first, such as the case of a bridge backwall with a roadway above it.

Quality Assurance

Quality assurance of all Cellofoam Elastic Inclusion EPS is confirmed by extensive independent and internal laboratory physical property testing.

In-house compressive strength testing to ASTM D1621 test specifications for Elastic Inclusion EPS is conducted at our Cellofoam Technical Center in Gainesville, Georgia using a universal test machine. We also test to ensure water absorption falls within specified limits and conduct periodic flame spread testing to confirm effectiveness of the fire retardant.

To learn more about our Elastic Inclusion EPS or place an order, please give us a call at 540-662-0882.

Warning: This product is combustible and if exposed to a fire of sufficient heat and intensity may burn rapidly. It should not be left exposed or inadequately protected. Long-term exposure (several months or more) to ultraviolet radiation will cause discoloration. Protect Cellofoam Elastic Inclusion from exposure to hydrocarbons, coal tar pitch, solvents, and solvent fumes. Consult specific instructions and applicable building codes for use of this product.

Cellofoam North America Inc. is an expanded polystyrene foam manufacturer and not an engineering consulting firm. Thus, it is beyond our scope to provide design services on the specific use for our products. Users of our EPS products, including Elastic Inclusion, should consult with appropriate engineering experts to determine the exact type and specifications of EPS required for their project to meet structural and other design requirements. The performance data herein reflects Cellofoam’s expectation based on tests conducted in accordance with recognized standard methods from both internal and independent test laboratories. The sale of these products shall be subject to Terms and Conditions of Sale, including those limiting warranties as set forth in Cellofoam’s invoices. No agent, employee, or representative of Cellofoam North America Inc. or its subsidiary or affiliated companies is authorized to modify this disclaimer.

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