G-3
ASTM D709 Grade G-3, D709 Type G-3
G-3 is a phenolic-resin woven-fabric industrial laminate to ASTM D709 (Grade G-3 / Type G-3), selected for mechanical strength and machinability rather than electrical performance.
Reference datasheet — G-3 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
What is G-3?
G-3 is a phenolic-resin woven-fabric industrial laminate to ASTM D709 (Grade G-3 / Type G-3), selected for mechanical strength and machinability rather than electrical performance. It is stocked as pressed sheet, rod and tube with about 250 MPa tensile strength and service to 130 °C, and is used for machined gears, bushings and spacers as well as punched washers. The resin system is a thermoset, so parts cannot be welded or hot-formed, the reinforcement is abrasive on tooling (machinability score 42), and edges absorb moisture along the weave unless sealed. Where electrical or dimensional performance matters more, G-10 or FR-4 is the usual substitute. G-3 has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 67% of composite grades. Its glass-transition temperature is 160°C (320 °F). G-3 has a tensile strength of 250 MPa (36.3 ksi), stronger than 50% of composite grades. Elongation at break is 1.5% and the elastic modulus is 18 GPa (2.61 Msi).
What is G-3 used for?
- gears and bushings
- mechanical spacers
- cold-punched washers
- low-voltage insulating parts
Advantages
- Low embodied carbon — 4.5 kg CO₂/kg, better than 79% of composite grades
Limitations
- Hard to polish — 25/100, worse than 76% of composite grades
G-3 properties
Typical room-temperature values; bars are the position among composite grades.
Physical4
G-3 has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 67% of composite grades. Its glass-transition temperature is 160°C (320 °F).
Mechanical12
G-3 has a tensile strength of 250 MPa (36.3 ksi), stronger than 50% of composite grades. Elongation at break is 1.5% and the elastic modulus is 18 GPa (2.61 Msi).
Thermal8
G-3 is rated for continuous service to 130°C (266 °F). It conducts heat at 0.3 W/m·K (0.173 BTU/hr·ft·°F), worse than 63% of composite grades. Thermal expansion is 15 µm/m·K (8.33 µin/in·°F).
Electrical7
G-3 is an electrical insulator with a dielectric strength of 14 kV/mm (355.6 V/mil) and a resistivity of 1×10¹⁰ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (72/100), worse than 58% of composite grades. UV resistance is poor.
Sustainability4
Producing a kilogram of G-3 takes about 78 MJ of energy and emits 4.5 kg of CO₂ — less than 87% of composite grades. Typical recycled content is 0%.
Manufacturability2
G-3's machinability is fair (42/100, better than 58% of composite grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the composite family
Yield strength against density for every composite grade FabDigit runs. G-3 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with G-3
Is G-3 easy to machine?
Machine dry with carbide or PCD tooling and high speed/low feed; glass cloth is highly abrasive and dust must be extracted — support the exit face to avoid delamination and edge breakout.
Can G-3 be welded?
Not weldable — thermoset; join by bolting, riveting or epoxy/phenolic adhesive bonding after abrading and degreasing.
Can G-3 be formed, bent or molded?
Supplied as fully cured pressed laminate; it cannot be hot-formed or cold-punched (unlike paper/cotton grades) and must be cut, drilled or milled to shape.
G-3 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| E-glass woven fabriccontinuous-filament glass cloth reinforcement | 50 – 65 | 58 |
| phenolic (phenol-formaldehyde) resinresole/novolac binder, fully cured | ≥ 35 (balance) |
What surface finishes work on G-3?
Edges are sealed with epoxy or varnish to limit moisture pickup along the weave; no plating or anodizing — paint only on abraded, primed surfaces.
Equivalent designations
Standards and trade names that resolve to G-3 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- D709 Grade G-3D709 Type G-3
- Also called
- NEMA G-3
How much does G-3 cost?
G-3 is a premium-cost composite ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
G-3 — frequently asked
What is G-3 used for?
G-3 is typically used for gears and bushings, mechanical spacers, cold-punched washers and low-voltage insulating parts. In short: mechanical-grade phenolic laminate; better machining than FR-4; punchable insulating washers.
What is the tensile strength of G-3?
G-3 has a typical tensile strength of 250 MPa (36.3 ksi) — stronger than 50% of composite grades.
Is G-3 easy to machine?
Not especially — machinability is rated fair (42/100, better than 58% of composite grades). Machine dry with carbide or PCD tooling and high speed/low feed; glass cloth is highly abrasive and dust must be extracted — support the exit face to avoid delamination and edge breakout.
Can G-3 be welded?
Not weldable — thermoset; join by bolting, riveting or epoxy/phenolic adhesive bonding after abrading and degreasing.
What surface finishes work on G-3?
Edges are sealed with epoxy or varnish to limit moisture pickup along the weave; no plating or anodizing — paint only on abraded, primed surfaces.
Can G-3 be formed, bent or molded?
Supplied as fully cured pressed laminate; it cannot be hot-formed or cold-punched (unlike paper/cotton grades) and must be cut, drilled or milled to shape.
What is the maximum service temperature of G-3?
G-3 is rated for continuous use to about 130°C (266 °F), and briefly to 180°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does G-3 cost?
G-3 is a premium-cost composite ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM D709 Standard Specification for Laminated Thermosetting Materials — ASTM International (2017)
- NEMA LI-1 Industrial Laminated Thermosetting Products — NEMA (1998)
- Engineered Materials Handbook Vol.2: Engineering Plastics — ASM International (1988)
- Glass-fabric phenolic laminate (G-3) technical data — industrial laminate producers (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.