---
title: "Polystyrene — density, melting point and properties"
description: "Polystyrene has a density of 1,050 kg/m³ (1,040–1,060). Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/polystyrene/
site: "At One Place"
---

# Polystyrene

**Density of polystyrene: 1,050 kg/m³ (1,040–1,060)**

1.05 g/cm³ · 65.5 lb/ft³

Cheap, glass-clear, dimensionally precise straight out of the mould, and brittle enough that it cracks rather than bends — the sound of a snapping CD case is polystyrene failing exactly as designed. High-impact polystyrene (HIPS) adds a few percent of rubber, which trades the clarity for toughness and produces the opaque version used in food packaging. It dissolves in limonene and in many solvents, which is how model kit cement works and why it must be kept away from flexible PVC.

## Properties

- **Density:** 1,050 kg/m³ (1,040–1,060) — 1.05 g/cm³
- **Tensile strength:** 35–55 MPa
- **Young's modulus:** 3.2 GPa
- **Thermal conductivity:** 0.14 W/(m·K)
- **Thermal expansion:** 70 µm/(m·K)
- **Floats in water:** No
- **Magnetic:** No

## What it is used for

- CD cases and disposable cutlery
- Model kits and scale figures
- Yoghurt pots and food trays (as HIPS)
- Petri dishes and lab consumables

## 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
- rigid polyurethane foam: 40 kg/m³
- Water — the float line: 1,000 kg/m³
- polystyrene: 1,050 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 |
| --- | --- | --- |
| rigid polyurethane foam | 40 kg/m³ | 0.04× |
| expanded polystyrene foam | 20 kg/m³ | 0.02× |
| air | 1.2 kg/m³ | 0.00× |
| polystyrene ← | 1,050 kg/m³ | 1.05× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

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

## Is it magnetic?

Polystyrene is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of polystyrene?

1,050 kg/m³ (1,040–1,060), or 1.05 g/cm³.

### Does polystyrene float?

No. At 1,050 kg/m³ it is denser than water.

### Is polystyrene magnetic?

Polystyrene is not a metal and has no ferromagnetic response.

## Related pages

- [Does polystyrene float?](https://atoneplace.net/does-it-float/polystyrene/)
- [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/)