Glass-Fiber Laminates
Glass-fiber laminates are woven E-glass cloth pressed in a thermoset resin — epoxy for G10, FR-4 and G11, silicone for G7, melamine for G5, polyester mat for GPO-3 — into rigid sheet, rod and tube that machines to ±0.1 mm. G10 is the reference: about 1.8 g/cm³, flexural strength around 400 MPa, compressive strength above 400 MPa, dielectric strength near 20 kV/mm and continuous service to about 130 °C, which is why it is the structural insulator of test fixtures, cryostats and switchgear. The NEMA LI 1 grade letters name the resin and the fabric: the resin sets temperature, flame rating and arc behaviour, the glass sets the strength.
Popular glass laminate grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Best for |
|---|---|---|---|---|---|
| G10 | 240 | 310 | 1.8 | Fair | Structural insulation, fixtures, cryogenic supports |
| FR-4 | 275 | 310 | 1.85 | Fair | Flame-rated glass-epoxy, UL 94 V-0 |
| G11 | 260 | 340 | 1.85 | Fair | Glass-epoxy for 150–180 °C service |
| G7 | 110 | 170 | 1.8 | Fair | Silicone-glass for 220 °C and arc resistance |
| G5 | 90 | 220 | 1.95 | Poor | Melamine-glass arc and track barriers |
| G10-ESD | 240 | 300 | 1.85 | Fair | Static-dissipative test fixtures and trays |
| GPO-3 | — | 70 | 1.85 | Fair | Low-cost arc-resistant switchgear sheet |
Choose glass laminates for
Structural electrical insulation — test fixtures, probe plates, busbar supports, transformer spacers, motor slot wedges; cryogenic supports and thermal breaks from 4 K up; arc chutes, phase barriers and switchgear panels; static-dissipative trays and handling tooling; stiffeners, spacers and wear plates where a metal would short, corrode or conduct heat.
Look elsewhere when
The part is loaded through the thickness or at a bolt without an insert (laminates crush and delaminate — add a bushing or use aluminum), it must run dry against steel as a bearing (Phenolic CE), it runs above 220 °C (mica-glass, ceramic or a polyimide laminate), stiffness-to-weight is the whole point (Carbon Fiber), it needs to be molded into a 3D shape rather than machined from sheet (a glass-filled PA66-GF30 or PBT-GF30 molding), or it is a thin printed-circuit substrate rather than a mechanical part.
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Glass laminate by application
- Test fixtures and probe plates
- G10 or FR-4 sheet, 6–25 mm, machined to ±0.1 mm with drilled and bushed hole patterns; G10-ESD for boards that carry live electronics.
- Insulation at temperature
- G11 or FR-5 to 180 °C for motor, transformer and heater hardware; G7 to 220 °C where arc resistance matters more than strength.
- Arc and track resistance
- G5, G-9 and GPO-3 for phase barriers, arc chutes and contactor housings — melamine and polyester-mat surfaces do not carbonize into a conductive track the way epoxy does.
- Cryogenic supports
- G10 is the standard tie-rod and thermal-break material from liquid helium up: low thermal conductivity, no embrittlement, and it holds bolt loads through the cool-down.
Working with glass laminate
- Machining
- Glass is abrasive — carbide dulls in minutes — so diamond-coated or PCD tooling, high spindle speed, sharp edges and full dust extraction are the rule. G10 and FR-4 hold ±0.1 mm routinely and ±0.05 mm on stable geometries; G7 and G5 are more brittle at edges. Tools exiting through the layup unsupported fray and delaminate the last plies: back up drilled holes and compression-route through cuts.
- Cutting and design
- Waterjet is the economical route for flat profiles in any thickness; laser cutting chars epoxy edges and is reserved for thin sheet. Load laminates in-plane, keep fastener holes at least 3 diameters from an edge, put a metal insert under every re-torqued bolt and expect through-thickness strength to be about a tenth of in-plane. Sheet thickness tolerance is ±5–10 %, so faces that need a precise thickness are machined on both sides.
- Bonding and joining
- Epoxy, acrylic and cyanoacrylate adhesives bond well to a lightly abraded surface; potting compounds and conformal coats adhere. Nothing here welds, forms or bends after cure — a G10 bracket is machined from block, not folded.
- Finishing and moisture
- Glass-epoxy absorbs 0.1–0.3 % water and grows slightly with it; seal machined edges with epoxy or conformal coat on precision parts and on anything wet. Melamine G5 takes up more and wants sealing outdoors. Surfaces can be painted or screen-printed; there is no plating or anodizing, and colour is the natural yellow-green of the laminate or the pigmented sheet (black, blue, natural) as supplied.
Other composite series
Glass-Fiber Laminates — frequently asked
What is glass laminate?
Glass-fiber laminates are woven E-glass cloth pressed in a thermoset resin — epoxy for G10, FR-4 and G11, silicone for G7, melamine for G5, polyester mat for GPO-3 — into rigid sheet, rod and tube that machines to ±0.1 mm. G10 is the reference: about 1.8 g/cm³, flexural strength around 400 MPa, compressive strength above 400 MPa, dielectric strength near 20 kV/mm and continuous service to about 130 °C, which is why it is the structural insulator of test fixtures, cryostats and switchgear. The NEMA LI 1 grade letters name the resin and the fabric: the resin sets temperature, flame rating and arc behaviour, the glass sets the strength.
Which grade of glass laminate should I use?
G10 for any machined insulator or fixture that must carry load — standoffs, terminal boards, busbar supports, cryogenic straps — and G10-ESD where electronics handling needs a static-dissipative surface. FR-4 when a flammability spec is in play: the same glass-epoxy with a brominated flame retardant to UL 94 V-0, so it is what circuit boards and most commercial fixtures are made of. G11 (and its flame-retardant twin FR-5) when the part runs at 150–180 °C, where G10 has gone soft. G7 silicone-glass for 220 °C and arc resistance at the cost of about two thirds of the mechanical strength; G5 and G-9 melamine-glass for the hardest, most arc- and track-resistant barriers in switchgear, accepting higher moisture uptake. GPO-3 glass-mat polyester is the low-cost, V-0, arc-resistant sheet for enclosures and phase barriers; CEM-1 and CEM-3 are the composite-core circuit-board laminates; 3240 is the Chinese epoxy-glass sheet of the G10 class.
Which grade of glass laminate is the strongest?
FR-4 has the highest yield strength in the series at 275 MPa; G11 follows at 260 MPa. Values are for each grade's default condition.
Which grade of glass laminate is easiest to machine?
FR-3 (machinability very good, 80/100), then FR-2 (75/100).
G10 or G11?
The same E-glass cloth in a higher-temperature epoxy: G11 keeps roughly half its flexural strength at 150 °C and is rated for continuous service to about 180 °C, where G10 is limited to about 130 °C and softens above it. Room-temperature strength and dielectric properties are near-identical and both machine the same way; G11 costs more. FR-5 is G11 with a UL 94 V-0 flame retardant, as FR-4 is to G10.
Why does G7 have lower strength than G10 if it takes more heat?
Because the binder is a silicone resin, not an epoxy: silicone survives 220 °C and does not carbonize under an arc, but it is a weak, flexible polymer that bonds less well to the glass, so flexural strength drops to roughly a third of G10 and the laminate delaminates more easily at machined edges. Use G7 where the electrical and thermal behaviour is the requirement and keep the mechanical load small or in compression.