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Comparison of Expanded Polystyrene and Extruded Polystyrene

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Dyplast is releasing this one-page Qwik Guide as an update on a general comparison between EPS and XPS. While EPS and XPS are both rigid, thermoplastic foam materials made from solid polystyrene, they are surprisingly different products with different applications and rarely compete. EPS is a closed cell foam and XPS is generally considered an open cell foam. Yet what are the actual implications in performance across various applications within in-situ environments? You will be surprised!

Expanded Polystyrene and Extruded Polystyrene

With respect to applications, EPS is often used as insulation within cold storage panels, insulated metal panels, and lightweight concrete roof applications. They can also be used as geofoam and in concrete forms as well as special shapes such as balusters, moldings, and columns that simulate concrete and wood at a fraction of the cost and weight. XPS, on the other hand, is more expensive and mostly utilized in limited cold pipe applications and as sheet insulation in buildings.

Expanded Polystyrene

To manufacture a block of EPS foam, polystyrene beads enter a large block mold where steam heats and expands the beads containing polystyrene, blowing agents, and additives. As pressure builds, the beads are tightly fused together. At Dyplast, our well-controlled process creates a solid, homogeneous block with excellent insulating qualities that do not degrade over time as well as excellent water resistance and compressive strength - meeting all requirements of ASTM C578. Densities are available at 1.0, 1.25, 1.5, and 2.0 lb/ft3. The large EPS blocks can be fabricated per specification to form insulation boards, blocks, or customized shapes for the roofing, insulated metal panels, and packaging industries.

Extruded Polystyrene

XPS foam is manufactured from solid polystyrene crystals. The crystals, along with special additives and a blowing agent, are fed into an extruder. The mixture is blended and melted under high temperature and pressure and becomes a viscous plastic fluid. The hot, thick liquid is then forced in a continuous process through a die. As it emerges from the die it expands to a foam, is shaped, cooled, and then trimmed to dimension. The size and shape of the die vary with the intended application. For instance, three common sizes of “billets” destined for fabricating pipe insulation shapes are: 7”x14”x108”; 8”x16”x108”; and 10”x20”x108” which is much smaller than EPS blocks. For wall insulation applications, XPS is typically extruded as 2ft by 8ft, or 4ft by 8ft sheets of varying thickness - commonly 2 inches.


While EPS and XPS each comply with ASTM C578 (Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation), care should be taken to evaluate how/whether each product may match the specific application. We caution that clients should examine advertised properties against third-party test results. Both EPS and XPS provide good insulating performance. For example, Type IX 1.8 lb/ft³ density EPS has a minimum R-Value of 4.2 versus 3.9 for the standard Type XIII 1.6 lb/ft³ XPS billets.

EPS is not a true closed cell foam and therefore typically has higher water absorption values measured per ASTM C272, and Dyplast does not recommend its use on lower temperature pipe insulation applications. XPS, while a more expensive product, is a closed cell foam and can be used in limited cold applications. Types XI, I, VIII, II, IX and XV typically are EPS and Types XII, X, XIII, I, VI, and V are XPS. Another advantage of EPS is that scrap or waste generated during manufacturing and fabrication, or at the end-use stage can be recycled into the molding process. At Dyplast, multiple levels of recycled materials are used.

To view the full Qwik Guide, click here.

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