G-9
ASTM D709 Grade G-9
G-9 is a melamine-resin glass-fabric laminate to ASTM D709 (Grade G-9), a higher-strength step up from G-5 with improved mechanical and electrical properties for switchgear duty.
Reference datasheet — G-9 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-9?
G-9 is a melamine-resin glass-fabric laminate to ASTM D709 (Grade G-9), a higher-strength step up from G-5 with improved mechanical and electrical properties for switchgear duty. It is available as sheet, thin sheet, rod and tube at about 240 MPa tensile strength, and is chosen where arc resistance and hard, non-tracking insulation are required. It is a thermoset — not weldable or formable after cure — and melamine-glass is hard on tooling, with a machinability score of 30, so allow for slow cutting and frequent tool changes. Where machining cost or moisture resistance dominates, G-10/FR-4 is the common alternative. G-9 has a density of 1.95 g/cm³ (0.0704 lb/in³), heavier than 75% of composite grades. G-9 has a tensile strength of 240 MPa (34.8 ksi), weaker than 51% of composite grades. The elastic modulus is 19 GPa (2.76 Msi).
What is G-9 used for?
- high-strength arc-resistant parts
- switchgear insulation
- circuit breaker housings
Limitations
- Hard to polish — 20/100, worse than 90% of composite grades
G-9 properties
Typical room-temperature values; bars are the position among composite grades.
Physical3
G-9 has a density of 1.95 g/cm³ (0.0704 lb/in³), heavier than 75% of composite grades.
Mechanical10
G-9 has a tensile strength of 240 MPa (34.8 ksi), weaker than 51% of composite grades. The elastic modulus is 19 GPa (2.76 Msi).
Thermal8
G-9 is rated for continuous service to 155°C (311 °F). It conducts heat at 0.32 W/m·K (0.185 BTU/hr·ft·°F), worse than 55% of composite grades. Thermal expansion is 14 µm/m·K (7.78 µin/in·°F).
Electrical7
G-9 is an electrical insulator with a dielectric strength of 12 kV/mm (304.8 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 64% of composite grades. UV resistance is fair.
Sustainability4
Producing a kilogram of G-9 takes about 100 MJ of energy and emits 6 kg of CO₂ — less than 67% of composite grades. Typical recycled content is 0%.
Manufacturability2
G-9's machinability is poor (30/100, worse than 54% 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-9 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with G-9
Is G-9 easy to machine?
Machine dry with carbide or PCD tooling, high speed and light feed; back up the exit side to avoid delamination and provide dust extraction (glass + melamine dust is abrasive and irritating).
Can G-9 be welded?
Not weldable — a thermoset; join by bonding with epoxy adhesives or by mechanical fastening with washers under bolt heads.
Can G-9 be formed, bent or molded?
Supplied fully cured; cold forming is not possible, so all shapes are produced by sawing, punching (thin gauges only, warmed), routing and drilling.
G-9 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 woven glass cloth reinforcement | 55 – 68 | 62 |
| melamine-formaldehyde resinmatrix; may contain minor cellulose-free fillers and cure catalysts | ≥ 32 (balance) |
What surface finishes work on G-9?
Edges should be deburred and sealed (epoxy varnish) in humid or high-voltage service to limit moisture pickup and surface tracking; no plating or anodizing applies.
Equivalent designations
Standards and trade names that resolve to G-9 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- D709 Grade G-9
How much does G-9 cost?
G-9 is a high-cost composite ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
G-9 — frequently asked
What is G-9 used for?
G-9 is typically used for high-strength arc-resistant parts, switchgear insulation and circuit breaker housings. In short: arc-resistant melamine glass; stronger than G-5; hard, non-tracking insulator.
What is the tensile strength of G-9?
G-9 has a typical tensile strength of 240 MPa (34.8 ksi) — weaker than 51% of composite grades.
Is G-9 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 54% of composite grades). Machine dry with carbide or PCD tooling, high speed and light feed; back up the exit side to avoid delamination and provide dust extraction (glass + melamine dust is abrasive and irritating).
Can G-9 be welded?
Not weldable — a thermoset; join by bonding with epoxy adhesives or by mechanical fastening with washers under bolt heads.
What surface finishes work on G-9?
Edges should be deburred and sealed (epoxy varnish) in humid or high-voltage service to limit moisture pickup and surface tracking; no plating or anodizing applies.
Can G-9 be formed, bent or molded?
Supplied fully cured; cold forming is not possible, so all shapes are produced by sawing, punching (thin gauges only, warmed), routing and drilling.
What is the maximum service temperature of G-9?
G-9 is rated for continuous use to about 155°C (311 °F), and briefly to 200°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does G-9 cost?
G-9 is a high-cost composite ($$$$), pricier than about 78% 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)
- IEC 60112 — Method for determining proof and comparative tracking indices — IEC (2020)
- Melamine-glass (G-5/G-9) industrial laminate datasheets — Laminate producers (e.g. Norplex-Micarta, Von Roll, Attwater) (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.