FR-3 vs FR-6
Composite · grade comparison
FR-3 and FR-6 are both composite grades. FR-3 is the stronger of the two: tensile strength 95 MPa (13.8 ksi) against 85 MPa (12.3 ksi) for FR-6, about 12% more. FR-3 is lighter (1.45 g/cm³ vs 1.85 g/cm³ for FR-6) and FR-6 is stiffer (10 GPa vs 9 GPa). On the shop floor, FR-3 machines more easily (very good vs fair).
FR-3Choose it when strength drives the design, or when weight is the constraint.
FR-6Choose it when the part sees heat.
FR-3 vs FR-6: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all composite 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 composite 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
Poisson's Ratio
Tensile Strength (Ultimate)
Compressive Strength
Flexural Strength
Flexural Modulus
Shear Strength
Izod Impact, Notched
Shear Modulus
Compressive Modulus
Same in both: Elongation at Break 1.2% · Hardness, Rockwell M 105 HRM
Physical
Density and transition temperatures.
Density
Glass Transition (Tg)
Water Absorption (24 h)
Water Absorption (Saturation)
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
Limiting Oxygen Index
Max Service Temperature (short-term)
Heat Deflection Temp. @ 1.8 MPa
Electrical
Conductivity and insulation.
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Comparative Tracking Index (CTI)
Same in both: Electrical Resistivity 1×10¹¹ Ω·m3.94×10¹⁸ µΩ·in · Volume Resistivity 1×10¹³ Ω·cm · Surface Resistivity 1×10¹² Ω
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
UV / Weathering Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Same in both: Polishability 20 / 100
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Water
Typical Recycled Content
Same in both: Embodied Carbon (primary production) 5 kg CO₂/kg
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 composite grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | FR-3 | FR-6 |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$ Premium | $$$ Premium |
| Min. machined wall | — | — |
| Best machined surface | — | — |
FR-3 vs FR-6 — frequently asked
Is FR-3 stronger than FR-6?
Yes. FR-3 has a typical tensile strength of 95 MPa (13.8 ksi) against 85 MPa (12.3 ksi) for FR-6 — about 12% more.
Which is cheaper, FR-3 or FR-6?
Both sit in the same relative cost tier ($$$, premium); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, FR-3 or FR-6?
FR-3. Its machinability rates very good (80/100) against fair (45/100) for FR-6.
Ready to make it?
Upload a CAD file and FabDigit prices the part in FR-3 and FR-6 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.