Quick answer: EPS does not have a single sharp melting point. It begins to soften and shrink around 90–100 °C, and the raw polystyrene itself melts at roughly 240 °C. In everyday service, EPS should be kept below about 75–80 °C to avoid dimensional change.

Why EPS has no single melting point

Expanded polystyrene is a foam, not a solid block of plastic. Much of its volume is trapped air inside thin polystyrene cell walls. So the temperature story has two parts: what happens to the foam structure and what happens to the polystyrene plastic itself.

The figure most designers need is the practical upper service limit: about 75–80 °C for standard EPS.

Why EPS shrinks when heated

When EPS is warmed above roughly 90 °C, the thin cell walls soften and the air inside the cells can escape. As the internal gas pressure is lost, the foam contracts and the part changes shape. This is why EPS should never be steam-cleaned, hot-washed or left in a hot car for long periods.

What this means in practice

Packaging and cold chain

Typical shipping and storage temperatures are far below the limit, so EPS packaging is completely safe in normal conditions.

Construction

EPS insulation sits behind wall and roof finishes and rarely approaches 70 °C. Where higher temperatures are possible, designers add a thermal break or choose a higher-grade foam.

Hot-fill or oven use

EPS is not suitable for hot-fill food containers or any application above about 75 °C. For heat resistance up to roughly 120 °C, EPP is the better material — see EPP molds.

EPS vs other foams on heat

The trade-off is cost: EPP costs more but tolerates heat far better. For a material-level comparison including density and impact, see EPS vs EPP material.

Processing temperature vs service temperature

Steam moulding deliberately heats EPS beads to fuse them, using steam around 110–140 °C for a brief moment inside a mould. This is a controlled, short process — quite different from continuous exposure in service. The steam chamber and mould tooling control that heat precisely.

Frequently asked questions

At what temperature does EPS melt?

The polystyrene polymer in EPS melts at about 240 °C, but the foam itself softens and shrinks from roughly 90–100 °C, so the practical limit for use is around 75–80 °C.

Does EPS burn?

Like all organic foams, EPS will burn if exposed to a sustained ignition source. Standard EPS ignites readily, which is why flame-retardant grades are specified for construction applications.

Can EPS be used in a hot car?

EPS is generally stable in a car interior, but leaving it against a hot surface or in extreme direct sun for long periods can cause gradual shrinkage. Packaged goods are usually fine.

What foam should I use above 80 °C?

EPP is the usual choice for service temperatures up to about 120 °C, combined with much better repeated-impact resistance.

Related products and guides

• Steam Chamber for EPS Mold
• EPP Mold Manufacturer
• The Difference Between EPS and EPP
• EPS Mold Manufacturer