---
title: "Borosilicate glass — density, melting point and properties"
description: "Borosilicate glass has a density of 2,230 kg/m³. Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/borosilicate-glass/
site: "At One Place"
---

# Borosilicate glass

**Density of borosilicate glass: 2,230 kg/m³**

2.23 g/cm³ · 139.2 lb/ft³

Adding boron oxide drops the thermal expansion coefficient from 9 to 3.3 µm/(m·K), and that single number is the entire reason it survives thermal shock. Thermal stress is proportional to expansion coefficient times temperature difference, so borosilicate tolerates roughly three times the temperature gradient of window glass before it cracks — which is why a Pyrex dish goes from oven to worktop and a drinking glass does not. Older Pyrex kitchenware was borosilicate; much of the modern US-sold product is tempered soda-lime instead, which fails differently.

## Properties

- **Density:** 2,230 kg/m³ — 2.23 g/cm³
- **Tensile strength:** 30–70 MPa
- **Young's modulus:** 64 GPa
- **Thermal conductivity:** 1.14 W/(m·K)
- **Hardness:** 6 Mohs
- **Thermal expansion:** 3.3 µm/(m·K)
- **Floats in water:** No
- **Magnetic:** No

## What it is used for

- Laboratory glassware
- Oven dishes and coffee pots
- Stage and vehicle lighting
- Telescope mirror blanks

## 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
- borosilicate glass: 2,230 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× |
| borosilicate glass ← | 2,230 kg/m³ | 2.23× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

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

## Is it magnetic?

Borosilicate glass is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of borosilicate glass?

2,230 kg/m³, or 2.23 g/cm³.

### Does borosilicate glass float?

No. At 2,230 kg/m³ it is denser than water.

### Is borosilicate glass magnetic?

Borosilicate glass is not a metal and has no ferromagnetic response.

## Related pages

- [Does borosilicate glass float?](https://atoneplace.net/does-it-float/borosilicate-glass/)
- [Soda-lime glass](https://atoneplace.net/material/soda-lime-glass/)
- [Tempered glass](https://atoneplace.net/material/tempered-glass/)
- [Fused quartz](https://atoneplace.net/material/fused-quartz/)

## Sources

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