What is Expanded Polystyrene Rigid Insulation?

Expanded polystyrene (EPS) is white rigid foam insulation that is 98% air. It’s often called beadboard because of its look, and is a “go-to” material for the construction industry and packaging. Expanded polystyrene rigid insulation is also a versatile, cost-effective, and energy-efficient insulation product. 

Expanded Polystyrene

How Expanded Polystyrene is Made

Polystyrene is one of the world’s most used plastics, with annual production totaling several million tons. It’s manufactured in a three-step process using styrene beads and pentane as a blowing agent.

  • Pre-expansion. Polystyrene beads are produced in a crude oil refinery. The beads are filled with a foaming agent called pentane at temperatures above 90 degrees Celsius. Pentane’s boiling point is between 8 degrees Celsius and 36 degrees Celsius. The heat causes the pentane to evaporate–leaving the polystyrene beads expanded 20 – 50 times their original size and filled with dead air.
  • Maturing/Stabilization. The beads are then stored for 6 – 12 hours to stabilize.
  • Molding. After stability is achieved, the beads are molded into large blocks (Block Molding Process) or molded into custom shapes (Shape Molding Process). The blocks are then into rigid foam board insulation, most often using a hot wire method.

Expanded Polystyrene Uses

Expanded polystyrene is 98% air and 2% plastic. The closed cell construction makes all that air quite sturdy–yet soft enough to protect electronic equipment during shipping.

Construction Uses of EPS

Expanded polystyrene has evolved into one of the most used, trusted, versatile, and flexible insulation materials in the world. It is a closed-cell foam with an R-value of R-3.6 per inch and adding plastic facing to the board increases the R-value to R-3.8.

Contractors use expanded polystyrene rigid foam to insulate walls, floors, roofs, and crawl spaces. It’s the filling of Structural Insulated Panels (SIP) and the insulation in Insulated Concrete Forms (ICF). Manufacturers also use it to create Exterior Insulation and Finish Systems (EIFS).

Floors, Walls, and Ceilings

Contractors often apply EPS over a building’s exterior sheathing – it insulates the entire home’s building envelope. The added insulation covers wall cavities and studs and seals wood-sheathing gaps, cracks, and holes. Contractors can fit it tightly around wall penetrations and seal it with closed-cell spray foam.

Since EPS doesn’t absorb moisture, it’s just as valuable below grade as is above grade. It’s ideal for below-grade applications, like basement walls, because water, fungus, mold, and rot do not detract from its performance. EPS is available in multiple densities and thicknesses, making it easy to achieve the required R-values to meet local building codes.

Expanded Polystyrene Rigid Insulation Facings

Expanded polystyrene rigid insulation is manufactured with different faces, such as aluminum foil, kraft paper, and polyethylene. Many are protective, but aluminum foil adds reflective insulation in the form of a radiant barrier to enhance the insulating value of the foam. Polyethylene facing acts as a vapor retardant and helps joint tape adhere better.

Exterior Insulation and Finish Systems (EIFS)

This attractive and versatile exterior finish system (EIFS) may not be possible without expanded polystyrene, which is attached to the exterior walls in multiple shapes and sizes to provide design flexibility, low maintenance, durability, and energy efficiency.

Insulating Concrete Forms (ICF)

Insulating concrete forms take the place of wood or metal forms for pouring concrete. ICFs are manufactured using 2.75” external walls held together by polypropylene ties. Unlike traditional concrete forms, ICFs remain in place after the concrete cures.

Insulated concrete forms provide excellent R-value and soundproofing. They are common in basements, exterior and interior walls. 

Structurally Insulated Panels (SIP)

Structurally insulated panels consist of expanded polystyrene sandwiched between two layers of oriented strand board (OSB). These walls are available from 4” – 12” thick, with an option to replace the OSB with other materials like plywood. 

SIP construction offers superior insulation because of the bonded polystyrene and gap, crack, and hole sealing. The system uses almost no studs–eliminating most thermal bridging. (The R-value of studs in the building envelope is around half of the R-value of the EPS.)

Structurally insulated panel houses offer great strength–often surpassing the typical load capabilities of stick-framed houses. Rough framing and finishing a SIP house is much quicker than standard framed houses.

Packaging and Other Uses

Manufacturers mold EPS to products, keeping them secure while in the package and during shipping. Some of the other versatile uses of expanded polystyrene include:

  • Packaging Peanuts.
  • CD Cases.
  • Disposable Cutlery.
  • Bottles and Lids.
  • Trays and Tumblers.
  • Fast Food Containers.
  • Disposable Razors.
  • Flotation Items such as rafts, docks, water toys, and life preservers.

EPS Recycling

Two percent of expanded polystyrene is a combination of carbon, hydrogen, and oxygen. The other 98% is air. It contains no chlorofluorocarbons and no hydrochlorofluorocarbons. EPS is 100% completely recyclable at all stages of its life cycle.

EPS Toxicity

Expanded polystyrene rigid insulation is non-toxic and will not leach chemicals into soil or water. It is safe for multiple types of packaging–including food, and doesn’t release harmful chemicals. EPS provides excellent long-term insulation value without toxicity.

Expanded polystyrene is not considered a fire hazard, but as with many products, applying enough heat for long enough will burn or melt EPS. Some manufacturers infuse their products with fire retardant to make them even safer.