Fused Silica vs N-BK7
Glass · grade comparison
Fused Silica and N-BK7 are both glass grades. Fused Silica is harder — 700 HV against 610 HV for N-BK7 — which matters for wear surfaces and threads. Fused Silica is lighter (2.2 g/cm³ vs 2.51 g/cm³ for N-BK7) and N-BK7 is stiffer (82 GPa vs 72 GPa).
Fused SilicaChoose it when surface hardness matters, or when weight is the constraint.
Fused Silica vs N-BK7: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all glass grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all glass grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Bulk Modulus
Poisson's Ratio
Compressive Strength
Flexural Strength
Shear Strength
Fracture Toughness (K_IC)
Hardness, Vickers
Hardness, Knoop
Same in both: Tensile Strength (Ultimate) 50 MPa7.3 ksi · Elongation at Break 0% · Hardness, Mohs 6
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Refractive Index
Same in both: Light Transmission 92% · Porosity 0%
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Same in both: Min Service Temperature -200°C-328 °F
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Volume Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Typical Recycled Content
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Thermal Diffusivity
Thermal Shock Resistance Index
Same in both: Specific Stiffness (E / density) 32.7 MN·m/kg
Strength versus weight
Yield strength against density for every glass grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | Fused Silica | N-BK7 |
|---|---|---|
| Default condition | Annealed Glass | Annealed Glass |
| Relative cost | $$ Standard | $$ Standard |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Fused Silica vs N-BK7 — frequently asked
What is the difference between Fused Silica and N-BK7?
Fused Silica and N-BK7 are both glass grades. Fused Silica is harder — 700 HV against 610 HV for N-BK7 — which matters for wear surfaces and threads. Fused Silica is lighter (2.2 g/cm³ vs 2.51 g/cm³ for N-BK7) and N-BK7 is stiffer (82 GPa vs 72 GPa).
Which is cheaper, Fused Silica or N-BK7?
Both sit in the same relative cost tier ($$, standard); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, Fused Silica or N-BK7?
N-BK7. Its machinability rates poor (18/100) against not recommended (10/100) for Fused Silica.
Ready to make it?
Upload a CAD file and FabDigit prices the part in Fused Silica and N-BK7 side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.