New: our G10 material guide covers the full grade family (G10/FR4/G11/FR5), typical properties, and NEMA / IEC EPGC / 3240 equivalents.
Quick Answer
G10 and FR4 are NEMA-grade epoxy fiberglass laminates — strong, dimensionally stable, and electrically insulating in dry conditions. Both machine cleanly into custom washers, spacers, and sleeves. The key difference: FR4 is the flame-retardant grade; G10 carries no flame rating.
- Continuous-use temperature: typically ~130 °C (266 °F), NEMA Class B range — confirm with the supplier datasheet for your lot
- Electrical insulation: reliable in dry conditions; humidity and contamination reduce surface resistivity — not for long-term wet or chemical immersion
- For parts: these properties matter when the washer sits under sustained clamp load in a warm enclosure — FR4/G10 will not creep like molded nylon
Properties That Matter for Washers and Spacers
When an engineer specifies G10 or FR4 for a washer, spacer, or insulating component, five properties drive the decision:
- Electrical insulation — the part must not conduct between the fastener and the assembly.
- Temperature capability — enclosures run warm; the material must hold up continuously, not just survive a peak.
- Flame rating — many panel and switchgear specifications require a flame-retardant grade.
- Compressive and flexural strength — washers sit under sustained clamping load and must not creep or crack.
- Machinability — the part is almost always cut to drawing, so clean, precise machining matters.
Exact values vary by manufacturer, resin system, sheet thickness, and batch. The table below is therefore qualitative with typical ranges where a number is safe to state; for any application governed by a standard or safety code, request the datasheet for the actual material lot.
Typical Property Comparison (Qualitative + Typical Ranges)
| Property | G10 | FR4 |
|---|---|---|
| Base construction | Woven glass fabric + epoxy resin | Woven glass fabric + epoxy resin |
| NEMA grade | G10 (NEMA LI 1) | FR4 (flame-retardant grade) |
| Flame rating | Not rated flame-retardant | Flame-retardant; meets NEMA FR4 requirements |
| Typical continuous-use temperature | NEMA Class B range, typically ~130 °C (266 °F); confirm with datasheet | NEMA Class B range, typically ~130 °C (266 °F); confirm with datasheet |
| Electrical insulation | Good to excellent in dry conditions | Good to excellent in dry conditions |
| Compressive / flexural strength | High for a polymer; does not creep like molded nylon | High for a polymer; does not creep like molded nylon |
| Machinability | Good; clean edges with carbide or diamond tooling | Good; clean edges with carbide or diamond tooling |
| Common names | G10, Garolite G10, NEMA G10 | FR4, flame-retardant G10 (informal) |
Published values for dielectric strength, glass transition temperature, and mechanical properties differ between suppliers. Treat any single number found online as a typical published range and verify it against the datasheet of the material actually supplied.
Electrical Isolation Notes
In dry conditions, both G10 and FR4 are reliable electrical insulators, which is why they are the default washer material in panels, busbars, and switchgear. Two practical cautions apply:
- Surface condition matters. Contamination, moisture films, or conductive dust on the washer surface can create leakage paths even when the bulk material insulates well. Clean, sealed assemblies perform best.
- Humidity reduces margin. Prolonged humid or wet service lowers surface resistivity. For high-voltage or safety-critical isolation, design to the datasheet values for the specific grade and thickness rather than generic figures.
Breakdown and dielectric values are deliberately not quoted here—they depend on thickness, conditioning, and test method, and a number copied from a random datasheet can be off by a wide margin for the lot you receive.
Temperature and Flame Rating
G10 and FR4 are thermoset laminates: they do not melt. As temperature rises toward the glass transition point, mechanical properties decline gradually, which is why continuous-use limits matter more than short-term peaks. Standard grades are typically rated around 130 °C (266 °F) for continuous electrical service, in the NEMA Class B range—confirm the specific grade with the supplier datasheet.
The flame difference is the defining split between the two grades: FR4 contains a flame-retardant additive and meets the NEMA FR4 grade, while G10 carries no flame rating. Panel builders and OEMs that specify flame-retardant materials should default to FR4. The FR4 vs G10 comparison walks through the selection logic in detail.
From Sheet Properties to Finished Parts
These properties only become useful once the sheet becomes a part. Washers, spacers, standoffs, and sleeves are CNC-machined or punched from standard laminate sheet, then finished to the drawing dimensions. Because the laminate is thermoset and dimensionally stable, the machined washer holds its thickness under clamping load and keeps its insulating gap over the life of the assembly—behavior that molded nylon parts cannot match in warm enclosures.
IncomePultrusion machines G10 and FR4 washers, spacers, and sleeves to drawing. The G10 and FR4 CNC machining page covers tooling, tolerances, and what to send for a quote. One boundary worth repeating: for long-term chemical, salt-water, or marine immersion, laminate is the wrong material—use a pultruded FRP washer instead (see the FRP washers guide).
Frequently Asked Questions
What is G10 made of?
G10 is a NEMA-grade laminate made from woven glass fabric saturated with epoxy resin, cured under heat and pressure. It is strong, dimensionally stable, and electrically insulating in dry conditions.
Is Garolite the same as G10?
Garolite is a commercial brand name for glass-reinforced epoxy laminates, and G10 is commonly sold under it. Not all G10 carries the Garolite brand; properties depend on the specific grade and manufacturer, so check the datasheet rather than the label.
Do G10 and FR4 have different properties?
Mechanically and electrically they are very similar. The meaningful difference is flame retardancy: FR4 is the flame-retardant grade. Choose FR4 when a flame rating is specified; otherwise G10 is typically the lower-cost option.
Do I need a datasheet for my application?
Yes, whenever the part is governed by a standard, a safety code, or a customer specification. Datasheet values are lot- and thickness-specific; generic published figures are fine for early design but not for final verification.
Is G10 suitable for outdoor, wet, or chemical exposure?
G10 tolerates normal outdoor weather and incidental moisture, but it is an electrical laminate, not a corrosion material. For continuous wet, chemical, or marine service, pultruded FRP washers are the appropriate choice.
Specify Your Parts
Share the operating conditions—temperature, flame requirements, voltage environment, and dimensions—and IncomePultrusion will confirm the right grade. Request a quote for custom G10 and FR4 washers, spacers, or sleeves through the quote request page.
