---
title: "Silicone rubber — density, melting point and properties"
description: "Silicone rubber has a density of 1,250 kg/m³ (1,100–1,500). Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/silicone-rubber/
site: "At One Place"
---

# Silicone rubber

**Density of silicone rubber: 1,250 kg/m³ (1,100–1,500)**

1.25 g/cm³ · 78.0 lb/ft³

Its backbone is silicon and oxygen rather than carbon, which is why it stays rubbery from about -60 °C to +230 °C where every carbon-based rubber has either frozen solid or decomposed. It is weak in tension — 5-10 MPa against natural rubber's 20-30 — so it is never used for drive belts or tyres. It is also permeable to gases, which rules it out for compressed-gas seals but is exactly what makes silicone contact lenses breathable.

## Properties

- **Density:** 1,250 kg/m³ (1,100–1,500) — 1.25 g/cm³
- **Tensile strength:** 5–10 MPa
- **Young's modulus:** 0.005 GPa
- **Thermal conductivity:** 0.2 W/(m·K)
- **Thermal expansion:** 250 µm/(m·K)
- **Floats in water:** No
- **Magnetic:** No

## What it is used for

- Oven and bakeware moulds
- High-temperature gaskets and O-rings
- Medical tubing and implants
- Sealant around baths and windows

## 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
- silicone rubber: 1,250 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× |
| silicone rubber ← | 1,250 kg/m³ | 1.25× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

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

## Is it magnetic?

Silicone rubber is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of silicone rubber?

1,250 kg/m³ (1,100–1,500), or 1.25 g/cm³.

### Does silicone rubber float?

No. At 1,250 kg/m³ it is denser than water.

### Is silicone rubber magnetic?

Silicone rubber is not a metal and has no ferromagnetic response.

## Related pages

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