---
title: "Polypropylene — density, melting point and properties"
description: "Polypropylene has a density of 905 kg/m³ (895–920). Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/polypropylene/
site: "At One Place"
---

# Polypropylene

**Density of polypropylene: 905 kg/m³ (895–920)**

0.91 g/cm³ · 56.5 lb/ft³

At 905 kg/m³ it floats in water, which is how recyclers separate it — polyethylene is the only other common plastic that does. Its unique property is the living hinge: a thin folded section of polypropylene survives millions of flexes without cracking, which is why every flip-top bottle cap is made from it. It resists boiling water and dishwashers, but almost nothing sticks to it — glue and paint both fail, and joining means welding or a mechanical fixing.

## Properties

- **Density:** 905 kg/m³ (895–920) — 0.91 g/cm³
- **Melting range:** 160–170 °C
- **Tensile strength:** 25–40 MPa
- **Young's modulus:** 1.5 GPa
- **Thermal conductivity:** 0.15 W/(m·K)
- **Thermal expansion:** 100 µm/(m·K)
- **Floats in water:** Yes
- **Magnetic:** No

## What it is used for

- Food tubs, kettles and microwave containers
- Car bumpers and battery cases
- Living hinges on flip-top caps
- Rope, twine and woven sacks

## 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
- polypropylene: 905 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 |
| --- | --- | --- |
| rigid polyurethane foam | 40 kg/m³ | 0.04× |
| expanded polystyrene foam | 20 kg/m³ | 0.02× |
| air | 1.2 kg/m³ | 0.00× |
| polypropylene ← | 905 kg/m³ | 0.91× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

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

## Is it magnetic?

Polypropylene is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of polypropylene?

905 kg/m³ (895–920), or 0.91 g/cm³.

### Does polypropylene float?

Yes. At 905 kg/m³ it is less dense than water's 1,000.

### Is polypropylene magnetic?

Polypropylene is not a metal and has no ferromagnetic response.

## Related pages

- [Does polypropylene float?](https://atoneplace.net/does-it-float/polypropylene/)
- [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/)
- [PTFE](https://atoneplace.net/material/ptfe/)
- [Rigid PVC](https://atoneplace.net/material/pvc-rigid/)
- [HDPE](https://atoneplace.net/material/hdpe/)
- [Epoxy resin](https://atoneplace.net/material/epoxy-resin/)

## Sources

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