Case Study / Geofoam

What is Geofoam?

Geofoam is a generic name for large blocks of foam used in geotechnical applications in place of soil. It has changed over time to also include applications where geofoam is used in place of concrete for forming or as lightweight structural fill. Geofoam can be manufactured by either an expanded polystyrene (EPS) molder or an XPS extruder. It is in a lightweight fill category all by itself, often call ultra-lightweight fill, since it only weighs between 1-3 pounds per cubic foot. There are 7 different material grades identified in ASTM D6817 that provide compressive resistance at 1% deformation ranging from 317 to 2678 pounds per square foot. The number of applications for geofoam grows every year as we increase our understanding of the benefits it provides.

Most geofoam projects use EPS rather than XPS based on the available thicknesses and cost savings. EPS in molded into blocks ranging from up to 40” thick, up to 70” wide and up to 288” long, while XPS is manufactured in sheets ranging from 1/2-4” thick, 48” wide and 96” long. EPS is inherently a less expensive material due to its relatively simple manufacturing process. Large EPS blocks are molded and then cut to required thicknesses versus XPS which is manufactured in sheets. Thicker EPS block sizes reduce installation cost to achieve the acquired thickness.
Geofoam is often used as a lightweight fill on plaza decks, interior planters, stadium seating and other project types. The underlying driver for choosing geofoam in these applications is its lightweight, yet strong nature. At densities between 1-3 pounds per cubic foot, nothing else comes close. The next closest option is flowable-fill and it weighs in at a minimum of 20 pounds per cubic foot. When comparing it to soil at 120 pounds per cubic foot and concrete at 140 pounds per cubic foot, you can really begin to appreciate the weight difference of geofoam to other types of fill. To put this in perspective, think of a football field which is 360’ x 160’, and suppose we will need fill, 1’ thick. Soil would weigh 5,760,000 pounds, while geofoam would weigh as little as 48,000 pounds depending upon material grade chosen. If your football field has soft soils underneath or utilities running through the fill area, geofoam is the way to go.

Another benefit of geofoam is its structural nature, since it is capable of supporting loads up to 2,678 pounds per square foot. It is often used as a structural fill on road embankments, under slabs of commercial buildings, and plaza decks. Note plaza decks were listed under both lightweight and structural because quite often it is being relied upon for both of those benefits; weight and load bearing capabilities. If you were to take the football field used in the previous example and were to add a 4” concrete load distribution slab on top of the geofoam you could support loads ranging from up to 2678 pounds per square foot depending upon the material grade chosen. Geofoams ability to support heavy traffic loads coupled with its lightweight nature is what makes it such a great fit for urban transportation projects.

To further clarify what geofoam is, versus other uses for expanded polystyrene, the intent of geofoam is to use the blocks as lightweight and/or structural fill, not for insulation purposes. It’s a time proven, ultra-lightweight, structural fill, with engineered properties that do not change over time. It is also a material that’s easy to modify on jobsites. With all the benefits geofoam provides, it’s no wonder more and more applications are added to its project list every day. Elevation® Geofoam is the tradename for RoadMax™, SlabMax™, and SoilMax™ manufactured by Atlas EPS.


The top picture shows Elevation® geofoam being used structurally, whereas the bottom picture depicts how lightweight Elevation® geofoam is to carry or maneuver.