---
title: "Expanded polystyrene foam — density, melting point and propert"
description: "Expanded polystyrene foam has a density of 20 kg/m³ (11–35). Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/eps-foam/
site: "At One Place"
---

# Expanded polystyrene foam

**Density of expanded polystyrene foam: 20 kg/m³ (11–35)**

0.02 g/cm³ · 1.2 lb/ft³

About 98% air by volume, which is why 20 kg/m³ is typical and why a large block can be carried in one hand — it is the lightest solid material in everyday use. A crash helmet liner works by crushing permanently, absorbing energy once, which is exactly why a dropped or crashed helmet is replaced even when it looks fine. It has no melting point worth quoting: the foam collapses and shrinks back towards solid polystyrene from around 100 °C.

## Properties

- **Density:** 20 kg/m³ (11–35) — 0.02 g/cm³
- **Tensile strength:** 0.2–0.5 MPa
- **Young's modulus:** 0.005 GPa
- **Thermal conductivity:** 0.033 W/(m·K)
- **Floats in water:** Yes
- **Magnetic:** No

## What it is used for

- Packaging inserts and cool boxes
- Cavity wall and floor insulation board
- Cycle and motorcycle helmet liners
- Concrete formwork voids

## How it compares

*Water is 1,000 kg/m³. Anything with a shorter bar than water floats in it.*

- air: 1.2 kg/m³
- expanded polystyrene foam: 20 kg/m³
- Water — the float line: 1,000 kg/m³
- tungsten: 19,250 kg/m³
- gold: 19,300 kg/m³
- platinum: 21,450 kg/m³

*Water is 1,000 kg/m³. Anything below that floats.*

| Material | Density | Relative to water |
| --- | --- | --- |
| air | 1.2 kg/m³ | 0.00× |
| expanded polystyrene foam ← | 20 kg/m³ | 0.02× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

Expanded polystyrene foam contains no iron, so it cannot rust. Whether it degrades depends on the material, not on oxidation.

## Is it magnetic?

Expanded polystyrene foam is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of expanded polystyrene foam?

20 kg/m³ (11–35), or 0.02 g/cm³.

### Does expanded polystyrene foam float?

Yes. At 20 kg/m³ it is less dense than water's 1,000.

### Is expanded polystyrene foam magnetic?

Expanded polystyrene foam is not a metal and has no ferromagnetic response.

## Related pages

- [Does expanded polystyrene foam float?](https://atoneplace.net/does-it-float/eps-foam/)
- [PLA](https://atoneplace.net/material/pla/)
- [ABS](https://atoneplace.net/material/abs/)
- [Acrylic (PMMA)](https://atoneplace.net/material/acrylic/)
- [Polycarbonate](https://atoneplace.net/material/polycarbonate/)
- [Polypropylene](https://atoneplace.net/material/polypropylene/)
- [PTFE](https://atoneplace.net/material/ptfe/)
- [Rigid PVC](https://atoneplace.net/material/pvc-rigid/)
- [HDPE](https://atoneplace.net/material/hdpe/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)