Borosilicate glass vs Fused silica
Borosilicate glass and Fused silica are genuine alternatives to one another — a choice somebody actually makes — and differ on 3 measured properties, density most clearly.
Borosilicate glass vs Fused silica
Borosilicate glass
Glass with boron in it, which barely changes size when heated — the reason an oven dish does not shatter and a drinking glass does.
Fused silica
Glass made of nothing but silica — almost no thermal expansion, transparent into the ultraviolet, and difficult enough to make that it is used only where nothing else will do.
| Property | Borosilicate glass | Fused silica |
|---|---|---|
| Density | 2.2–2.25 g/cm³ higher | 2.2 g/cm³ |
| Refractive index | 1.47 higher | 1.458 |
| Thermal conductivity | 1.1–1.2 W/(m·K) | 1.38 W/(m·K) higher |
Choosing between them
Fused silica is recorded as a substitute for Borosilicate glass — better at temperature.
What it gives up: Melts above 1700 °C and is correspondingly expensive; it is used where borosilicate is not enough rather than where it would merely be better.
In this application, on the evidence cited above.