Frequently Asked Questions

Q:  What is EPS Geofoam?

    Expanded polystyrene (EPS) is a very common product that is widely used for packaging and in building construction. Manufacturing of EPS blocks begins with expandable polystyrene resin beads that are generally less than 3 mm in diameter and contain microscopic cells filled with a blowing agent. The usual blowing agents are pentanes or butanes and constitute about 5 percent of the bead weight. When exposed to steam under controlled pressure, the cell walls soften and the blowing agent expands. Individual resin beads enlarge by up to 40 times in volume to form pre-puffs. After a holding period to allow stabilization at at room temperature, the pre-puffs are poured to fill a recangular molding box. All six sides of the mold are fixed and more steam is injected through small perforations along the confining walls. The pre-puff in the molding box further expand and fuse to form a block. Geofoam blocks should be manufactured using modified beads that contain fire retardant additives. Commonly manufactured EPS block densities and dimensions with type designation per ASTM-C-578 are given below:

Type Density kg/m3 (pcf)
I 15 (0.90)
II 22 (1.35)
VIII 18 (1.15)
IX 29(1.80)
XI 12 (0.70) Rarely Produced

    An EPS molder (manufacturer) can produce blocks of a standard size that is characteristic for the molding equipment at the plant. The range of block dimensions that can be manufactured in different plants are the following:

Dimension size, mm (in)
width 305 to 1219 (12 to 48)
Length 1219 to 4877 (48 to 192)
Height 9.5 to 610 (3/8 to 24)

    EPS geofoam can also be formed to desired shapes by subjecting the pre-puff to steam and pressure in a shaping mold. Block or shape molded EPS can be used as produced or can be further cut either at the plant or in the field to desired dimensions.

Q:  What is XPS Geofoam?

    Extruded polystyrene (XPS) foam begins with polystyrene pellets. The resin is fed into an extruder where it is melted and mixed with critical additives to form a viscous molten mixture. A blowing agent is then injected to enable expansion. Under controlled heat and pressure conditions, the mixture is forced through a die into the desired shape. The rigid foam is trimmed to the final product dimensions. Commonly manufactured XPS board dimensions and densities classified by Type in ASTM-C-578 are as given below: 

Type Density kg/m3 (pcf)
IV 26 (1.60)
V 48 (3.00)
VI 29 (1.80)
VII 35 (2.20)
X 22 (1.35)

    XPS geofoam types listed above are manufactured in the following possible sizes:

Dimension Size, mm (in)
Width 406 to 1219 (16 to 48)
Length 1219 to 2743 (48 to 108)
Thickness 13 to 102 (0.5 to 4)

    Like EPS, XPS can be used as light weight fill soil substitute. To date, XPS board stock has been used more often for foundation and subgrade insulation.

Q:  Is geofoam flammable?

    Fire Hazard  :     Regular EPS and XPS products are combustible and protecting against fire hazard is an important consideration. Both EPS and XPS geofoam types should be specified to be manufactured using base materials that contain retardant additives. Even with retardant additives, storage and handling of geofoam blocks should be done with attention to fire safety.

Q:  How long has geofoam been used?

    Geofoam has been used for insulation and light weight fill applications for over 25 years. EPS blocks exhumed from a construction site in Norway after more than 20 years of burial were found to be in good condition and were re-used.

Q:  How is geofoam handled and installed?

    Geofoam blocks or boards are large but easy to handle. Construction with geofoam is rapid. For large volume applications, manufacturers may need adequate lead time to produce a sufficient quantity for a job. Geofoam shipments are usually installed on delivery without requiring on-site stockpiling or storage.Individual geofoam blocks or boards can be lifted by construction equipment and placed manually by a work crew. Smaller shapes and sizes required at the job site can be cut by either a chain saw or, more conveniently, by hot wire. The placement of geofoam blocks should be staggered to interlock and joints between block layers should not be made continuous. In handling and placement, care should be exercised to limit damage to geofoam blocks. Equipment that imposes high contact stresses should not be operated directly on the geofoam surface or over a thin lift above the geofoam.

Q:  Can geofoam be recycled?

    EPS waste generated in manufacturing plants is schredded and added to pre-puff to make geofoam blocks. Schredded foam or re-grind may constitute about 5 percent or more of geofoam block content. This re-cycling does not involve chemical processing. It is also possible a greater percentage of re-grind may be allowed in making geofoam for some applications. So far, the extent of recycling has mainly involved use of re-grind or plant generated waste from cutting and trimming. EPS geofoam recovered from previous jobs has also been re-used.

Q:  Does geofoam use have environmental impact?

    Operation of machinery and haul trucks at construction sites may involve some amount of oil and fuel spilling. There would also be increased air pollution from both construction activity and traffic slow down. Soil embankments require construction in thin lifts with repeated compaction. There is no need for compacting geofoam and each block is equivalent to four or more lifts in height. Erosion by surface runoff and dust generated from the construction area would be reduced. Construction with geofoam is much shorter in duration and can occur in any season. Geofoam is not biodegradable and once installed below surface there are no adverse effects on soil and groundwater quality. The manufacture of EPS geofoam does not involve use of gases that are known to be harmful to the environment. Overall, there would be reduced environmental impact by using geofoam than would be with earth construction.

Q:  How is EPS geofoam manufactured?

Glossary of common terms.

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