G10 / FR4 (Glass-Epoxy Laminate)
Also: G-10, FR-4, FR4, G10/FR4, glass epoxy, epoxy glass laminate, fiberglass sheet, NEMA G-10, GEE / GEE-F (MIL-I-24768), G-11 (high-temperature grade), FR-5, G-10CR (cryogenic), Garolite
G10 and FR4 are woven glass-epoxy laminates: stiff, strong, stable electrical insulators; FR4 is flame-retardant. Abrasive to machine; control the dust.
Sourcing G10 parts or stock?
- Machine shops that work with composites · 121
- Waterjet Cutting companies that work with composites · 19
- All U.S. manufacturers working with composites · 723
At a glance
| Density | 1.85 g/cm³ (0.067 lb/in³) |
|---|---|
| Tensile strength | 240-310 MPa (35-45 ksi) in the plane of the laminate, lengthwise; crosswise about 10-20% lower |
| Yield strength | n/a (a glass-fiber composite: essentially linear to fracture, with no yield point) |
| Hardness | Rockwell M 105-115 |
| Elongation | About 1-3% at break (brittle composite) |
| Modulus of elasticity | 17-19 GPa (2.5-2.7 Msi) flexural, lengthwise; about 15 GPa (2.2 Msi) crosswise; much lower through the thickness |
| Thermal | Thermoset, does not melt; epoxy Tg about 120-140 °C (250-285 °F) for standard G10 and FR4, about 170 °C (340 °F) for high-Tg FR4; continuous service about 130 °C (266 °F), G-11 and FR-5 to about 150-170 °C (300-340 °F); in-plane expansion about 10-15 um/m·K |
| Composition | Continuous woven E-glass fabric in a cured epoxy resin binder, laminated under heat and pressure (roughly 55-65% glass by weight); FR4 adds a flame-retardant, usually brominated, epoxy |
Typical values, Flat sheet to NEMA grade G-10 / FR-4, natural color, tested in the plane of the laminate at 23 °C (73 °F). Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- Holds tight tolerances (±0.05 mm, ±0.002") because it is stiff and stable, but it destroys tools: use diamond-coated carbide or PCD, rigid setups, and backing to stop edge fraying and delamination. Cut wet or with dust extraction; the dust irritates lungs and skin.
- WeldabilityFair
- A thermoset: it cannot be welded or solvent bonded. It bonds very well with epoxy and structural adhesives after scuff sanding and a solvent wipe, and tapped threads and inserts hold well in the face of the sheet.
- FormabilityNot recommended
- Cured thermoset laminate cannot be thermoformed, bent or reshaped. Parts are cut from flat sheet, rod or tube; curved or molded shapes must be laminated to shape by the producer.
- Corrosion resistanceGood
- Resists water (about 0.1-0.25% absorption in 24 hours), oils, fuels, most solvents and dilute acids. Strong acids and alkalis attack the resin and glass over time. Cut edges can wick moisture along the fibers, so seal edges on high-voltage parts in humid service. UV yellows the surface.
G10 is a thermoset composite: layers of woven E-glass cloth impregnated with epoxy resin and cured under heat and pressure into sheet, rod and tube. It is far stronger and stiffer than any unfilled plastic (in-plane tensile strength around 240-310 MPa, 35-45 ksi, and a flexural modulus near 17-19 GPa), absorbs very little water, holds its dimensions through temperature and humidity changes, and is an excellent electrical insulator. It is used for insulators, standoffs, terminal boards, switchgear barriers, washers, fixtures, cryogenic supports and knife handles.
FR4 is the flame-retardant version (UL 94 V-0, usually with a brominated epoxy) and is the base material of nearly every rigid printed circuit board, where it is bought copper-clad to IPC-4101. For machined parts, G10 and FR4 are close to interchangeable, and many suppliers sell sheet certified to both. G-11 and FR-5 use higher-temperature epoxy systems for service to roughly 150-170 °C (300-340 °F); G-10CR is a cryogenic-rated G10 used in superconducting magnets and cryostats.
Two things make G10 unusual in a machine shop. It is extremely abrasive: the glass dulls high-speed steel almost at once and carbide quickly, so diamond-coated or PCD tools are the norm in production. And its dust is a hazard: fine glass and epoxy particles irritate skin, eyes and lungs, and they wear machine ways and spindles. Shops cut it wet or with dedicated dust extraction, and many quote it only on machines set up for composites. It is also anisotropic, much weaker through the thickness than in the plane, so it delaminates under loads that peel the layers apart.
Heat treatment
None: it is a fully cured thermoset, and the producer does any post-cure. Parts for vacuum, high-voltage or soldering service are sometimes baked dry at about 100-120 °C (212-250 °F), below Tg, to drive out absorbed moisture. Do not heat above Tg.
Tempers and conditions
- G-10 (natural, not flame-retardant)
- FR-4 (flame-retardant, UL 94 V-0)
- G-11 (high-temperature epoxy)
- FR-5 (high-temperature, flame-retardant)
- Black and colored G-10
- Copper-clad FR-4 (PCB laminate)
- G-10CR (cryogenic)
Stock forms
- Sheet and plate
- Rod (rolled or molded)
- Tube (rolled or filament-wound)
- Copper-clad laminate
- Machined and punched parts
Relative cost
Tier 3 of 5. Roughly 2-4x acetal per pound for sheet; machining is the larger cost because of tool wear, dust control and the need for a shop set up for composites.
Typical applications
- Electrical insulators, standoffs, barriers and terminal boards
- Printed circuit board substrates (FR-4)
- Motor and transformer slot wedges, spacers and coil supports
- Washers, bushings and thermal-break spacers
- Cryogenic supports and structural parts (G-10CR)
- Test fixtures and electronics assembly nests
- Knife handles and sporting goods
Process compatibility
How G10 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | Machines to tight tolerances with diamond-coated or PCD tools and dust control; tool wear, not cycle time, drives the price. |
| CNC Milling | FairFair | Profiled from sheet with diamond-coated compression routers that keep both faces from fraying; wet cutting or extraction required. |
| CNC Turning | FairFair | Rod and tube turn into bushings and spacers, but edges chip and the laminate can peel at the ends; use PCD tooling and light finishing passes. |
| Waterjet Cutting | GoodGood | No dust, no heat, no tool wear: a good way to profile thick plate. Pierce at low pressure or pre-drill to avoid delaminating around the start hole. |
| Laser Cutting | PoorPoor | UV lasers depanel thin PCB laminate, but CO2 cutting chars the epoxy and leaves a carbonized, conductive edge that is unacceptable on insulators. Waterjet or rout instead. |
| Metal Stamping | FairFair | Thin sheet, up to about 1.6 mm (1/16"), can be punched or blanked, often warm, for washers and insulators; thicker stock cracks and delaminates at the edge. |
| Injection Molding | Not recommendedNot recommended | A cured laminate cannot be molded. For molded glass-filled insulators, use glass-filled nylon, PBT or a thermoset molding compound. |
| Bead Blasting | FairFair | A light scuff blast prepares surfaces for bonding; heavier blasting exposes and frays the glass weave. |
Design and sourcing tips
- Say G-10 or FR-4 on the drawing, and G-11 or FR-5 for heat. If flammability matters (UL 94 V-0), specify FR-4.
- Run loads in the plane of the laminate. Through-thickness tension and peel delaminate it, and threads or inserts placed in the edge of thin sheet split the layers.
- Sheet is supplied to a laminate thickness tolerance, not a machined one; call out a machined thickness only where it matters.
- For high-voltage insulators, specify sealed machined edges and forbid laser-cut edges, which can carry a conductive carbon track.
- Say it is G10 on the RFQ: not every shop will machine it, because of tool wear and dust.
- Consider PEEK or Ultem instead if the part must be molded, used in steam or strong chemicals, or bonded without surface prep.
Frequently asked questions
- What is the difference between G10 and FR4?
- Both are woven glass-epoxy laminates with nearly the same mechanical and electrical properties. FR-4 adds a flame retardant (usually brominated epoxy) and meets UL 94 V-0; G-10 does not. FR-4 is also the standard PCB substrate. For machined insulators and structural parts, many sheets are sold certified to both grades; specify FR-4 whenever flammability is a requirement.
- Is G10 dust dangerous?
- Machining G10 makes fine glass and epoxy dust that irritates the skin, eyes and lungs, and FR-4 dust also carries the flame-retardant chemistry. Shops cut it wet or with local exhaust and HEPA filtration, and operators wear respirators and protective clothing. The dust is also abrasive enough to wear machine ways, which is why many shops use dedicated equipment.
- Can G10 be machined?
- Yes, to tight tolerances, but it is very abrasive. High-speed steel dulls almost immediately; carbide works for short runs, and diamond-coated or PCD tools are used in production. Rigid setups, backing plates and compression routers keep edges from fraying. Expect a higher price than for a plastic part of similar size because of tooling and dust control.
- Is G10 a good electrical insulator?
- Yes. It has high dielectric strength (roughly 20-30 kV/mm, 500-800 V/mil, through thin sheet), low moisture absorption, and keeps its insulating properties in humid conditions better than paper or cotton phenolic laminates. Its arc resistance is modest, so for arcing and tracking service, specify an arc-track-resistant laminate such as GPO-3.
- Is G10 stronger than aluminum?
- In the plane of the sheet its tensile strength (about 240-310 MPa, 35-45 ksi) is comparable to 6061-T6 aluminum at about two-thirds of the density. But its stiffness is about a quarter of aluminum, it is weak through the thickness, and it fails by fracture rather than yielding. It is chosen for insulation and stability, not as a metal replacement.
Processes that commonly use it
Related materials
Where to verify these values
- NEMA LI 1 and ASTM D709
- MIL-I-24768 and IPC-4101
- Laminator data sheets (Norplex-Micarta and other NEMA-grade producers)
- ASTM D638, D790 and D149 (dielectric strength) test methods
