Polystyrene

Summary

Polystyrene is a thermoplastic from styrene, foamed into expanded (EPS) and extruded (XPS) insulation boards that are 95 to 98 percent air. It gives low-cost closed-cell insulation, but it is easily ignited and needs flame retardant and, for XPS, attention to blowing agents.

Cols

Image

EPS: expanded polystyrene, molded from beads
XPS: extruded polystyrene, continuous board
Blowing agent: gas that expands the foam; XPS has used HFC-134a
Graphite EPS: EPS with graphite filler for lower conductivity

History and demand

Invention

1839: Eduard Simon first isolated polystyrene in Berlin
1931: I.G. Farben began production in Ludwigshafen
1935: Munters and Tandberg patented polystyrene foam insulation (US 2,023,204)
1954: Koppers developed EPS under the Dylite name

Sourcing

Asia-Pacific accounted for about 57 percent of global expandable polystyrene demand in 2022 (Ceresana); China has the largest EPS capacity share (GlobalData)

Composition and production

Raw materials

Styrene polymer; foams are 95 to 98 percent air

Properties

Physical

Solid density: 0.96 to 1.05 g/cm3 (60 to 66 lb/ft3)
EPS density: 11 to 32 kg/m3 (0.7 to 2.0 lb/ft3); 21.6 to 28.8 kg/m3 for insulated concrete forms
XPS density: about 28 to 34 kg/m3 (1.7 to 2.1 lb/ft3)
Glass transition: about 100°C (212°F)

Thermal and moisture

Thermal conductivity: EPS 0.032 to 0.038 W/(m·K), about R-3.8 to R-4.5 per inch; graphite EPS about 0.029; XPS 0.029 to 0.039, average 0.035 (about R-4.1 per inch)
Vapor diffusion resistance (mu): EPS 30 to 70; XPS 80 to 250

Fire behavior

EPS limiting oxygen index about 18 percent; ASTM C578 requires more than 24 percent, so flame retardant is added
Flame-retarded boards: flame spread index below 25 and smoke-developed index below 450 in tunnel testing
Classed DIN 4102 B3 (easily ignited)

Standards

Material specifications

ASTM C578: rigid cellular polystyrene thermal insulation

Uses in buildings

Building elements

Wall and Roof Insulation: EPS and XPS board
Insulated concrete forms use EPS

Pros and cons

Pros

Low thermal conductivity at very low density
XPS has higher vapor resistance than EPS

Cons

Easily ignited; needs flame retardant
XPS blown with HFC-134a has a global warming potential of about 1,000 to 1,300 times CO2

Sustainability

Embodied carbon

CO2-blown XPS has ozone depletion potential 0 and global warming potential below 5; the EU banned HFC-134a from 2022

Recycled content and end of life

Compaction raises EPS scrap density from about 30 to 330 kg/m3

Health

Burning at 800 to 900°C yields over 90 compounds

Manufacturing and cost

Main manufacturers and suppliers

Trade association: EPS Industry Alliance.

Sources

Wikipedia: Polystyrene, https://en.wikipedia.org/wiki/Polystyrene
Wikimedia Commons: Polistirolo.JPG, photo by Phyrexian (CC BY-SA 3.0), https://commons.wikimedia.org/wiki/File:Polistirolo.JPG
Ceresana: expanded polystyrene market report, https://ceresana.com/en?p=3352