KDP vs Sapphire
Glass · grade comparison
KDP and Sapphire are both glass grades. Sapphire is the stronger of the two: tensile strength 400 MPa (58 ksi) against 12 MPa (1.74 ksi) for KDP, about 33 times as much. Sapphire is harder — 2,000 HV against 170 HV for KDP — which matters for wear surfaces and threads. KDP is lighter (2.34 g/cm³ vs 3.98 g/cm³ for Sapphire) and Sapphire is stiffer (400 GPa vs 44 GPa). On the shop floor, KDP machines more easily (poor vs not recommended) and Sapphire sits in a lower cost tier (standard, $$) than KDP (high, $$$$).
KDPChoose it when weight is the constraint, or when the part is machined in volume.
SapphireChoose it when strength drives the design, or when surface hardness matters.
KDP vs Sapphire: 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)
Compressive Strength
Flexural Strength
Shear Strength
Fracture Toughness (K_IC)
Hardness, Vickers
Hardness, Knoop
Hardness, Mohs
Same in both: Elongation at Break 0%
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Refractive Index
Light Transmission
Same in both: 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)
Min Service Temperature
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)
Specific Stiffness (E / density)
Thermal Diffusivity
Thermal Shock Resistance Index
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 | KDP | Sapphire |
|---|---|---|
| Default condition | — | Annealed Glass |
| Relative cost | $$$$ High | $$ Standard |
| Min. machined wall | — | — |
| Best machined surface | — | — |
KDP vs Sapphire — frequently asked
Is Sapphire stronger than KDP?
Yes. Sapphire has a typical tensile strength of 400 MPa (58 ksi) against 12 MPa (1.74 ksi) for KDP — about 33 times as much.
Which is cheaper, KDP or Sapphire?
Sapphire is the lower-cost material: it sits in the standard tier ($$) while KDP is high ($$$$). 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, KDP or Sapphire?
KDP. Its machinability rates poor (30/100) against not recommended (5/100) for Sapphire.
Ready to make it?
Upload a CAD file and FabDigit prices the part in KDP and Sapphire 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.