KCl vs N-BK7
Glass · grade comparison
KCl and N-BK7 are both glass grades. N-BK7 is the stronger of the two: tensile strength 50 MPa (7.25 ksi) against 2 MPa (0.348 ksi) for KCl, about 21 times as much. In exchange, KCl is the more ductile: elongation 2% versus 0% for N-BK7, and N-BK7 is harder (610 HV vs 9 HV). KCl is lighter (1.98 g/cm³ vs 2.51 g/cm³ for N-BK7) and N-BK7 is stiffer (82 GPa vs 29.7 GPa). On the shop floor, KCl machines more easily (good vs poor) and N-BK7 sits in a lower cost tier (standard, $$) than KCl (high, $$$$).
KClChoose it when the part is bent, formed or impact-loaded, or when weight is the constraint.
N-BK7Choose it when strength drives the design, or when cost is the deciding factor.
KCl 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
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Flexural Strength
Shear Strength
Fracture Toughness (K_IC)
Hardness, Vickers
Hardness, Knoop
Hardness, Mohs
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)
Min Service Temperature
Same in both: Max Service Temperature (continuous) 500°C932 °F
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Constant (1 MHz)
Volume Resistivity
Dielectric Strength
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)
Typical Recycled Content
Embodied Water
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Thermal Diffusivity
Same in both: Thermal Shock Resistance Index 0
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 | KCl | N-BK7 |
|---|---|---|
| Default condition | — | Annealed Glass |
| Relative cost | $$$$ High | $$ Standard |
| Min. machined wall | — | — |
| Best machined surface | — | — |
KCl vs N-BK7 — frequently asked
Is N-BK7 stronger than KCl?
Yes. N-BK7 has a typical tensile strength of 50 MPa (7.25 ksi) against 2 MPa (0.348 ksi) for KCl — about 21 times as much.
Which is cheaper, KCl or N-BK7?
N-BK7 is the lower-cost material: it sits in the standard tier ($$) while KCl is high ($$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which is easier to machine, KCl or N-BK7?
KCl. Its machinability rates good (60/100) against poor (18/100) for N-BK7.
Ready to make it?
Upload a CAD file and FabDigit prices the part in KCl 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.