FR4 vs G10: Which Epoxy Fiberglass for Washers & Parts?

New: our G10 material guide covers the full grade family (G10/FR4/G11/FR5), typical properties, and NEMA / IEC EPGC / 3240 equivalents.

Overview

FR4 and G10 are both NEMA-grade epoxy fiberglass laminates. They share a similar construction—woven glass fabric saturated with epoxy resin and cured under heat and pressure—but they are not identical. The main difference is the flame-retardant additive in FR4, which makes it the preferred choice when fire resistance is required.

This comparison focuses on how the two materials perform as washers, spacers, and small CNC-machined parts. It also explains when each grade is the better fit and how both differ from pultruded FRP washers used in corrosive environments.

What Are G10 and FR4?

G10 is a general-purpose epoxy fiberglass laminate defined by NEMA LI 1. It offers high mechanical strength, good dimensional stability, and electrical insulating properties. FR4 is a flame-retardant version of the same laminate family. It meets the NEMA FR4 specification and is widely used in electrical and electronic applications where flammability is a concern.

Both materials are supplied as sheets, rods, and tubes. For washers and spacers, flat sheets are CNC-machined or punched to the required ID, OD, and thickness. The finished parts are lightweight, non-conductive, and resistant to moisture in normal indoor conditions.

Because G10 and FR4 are thermoset laminates, they do not melt when heated. Instead, they gradually lose mechanical properties as temperature approaches the glass transition point. This makes them stable in warm enclosures, but it also means that continuous-use limits should be confirmed from the supplier datasheet rather than assumed.

NEMA Grades and Standards

NEMA (National Electrical Manufacturers Association) publishes the standard grades used to specify epoxy fiberglass laminates in North America. G10 is covered by NEMA LI 1, while FR4 is covered by the same family with additional flame-retardant requirements. These grades describe minimum mechanical, electrical, and thermal performance, but they do not define every property for every thickness or supplier.

When ordering machined parts, the drawing should state the required grade, sheet thickness, and any flame or electrical requirements. If the assembly is governed by a local safety or electrical code, the end customer should confirm that the selected grade and supplier documentation meet that code.

FR4 vs G10 Comparison

Exact values for glass transition temperature, dielectric strength, and flame rating vary by manufacturer, sheet thickness, and batch. Always request a datasheet for applications governed by specifications.

Key Material Properties

Both G10 and FR4 combine high strength with low weight because the woven glass reinforcement carries most of the mechanical load while the epoxy matrix binds the fibers and protects them from moisture and handling damage.

• Compressive strength: High enough for bolt clamp loads and spacer applications in electrical assemblies. The exact value depends on fiber orientation and sheet thickness.
• Dimensional stability: Low moisture absorption helps machined washers retain their thickness and ID/OD tolerances in normal indoor conditions.
• Electrical insulation: Both grades are non-conductive in dry environments, making them suitable for isolating bolts from frames, busbars, and enclosures.
• Temperature behavior: NEMA Class B ratings typically point to a continuous-use temperature around 130 °C (266 °F), but the usable limit depends on load, exposure time, and the specific resin system.
• Chemical resistance: Resistant to moisture and many common industrial fluids in indoor service, but not intended for long-term immersion in aggressive chemicals.

For the supplier-specific numbers needed for a drawing or material approval, request a batch datasheet or certificate of conformance.

Machining and Tolerances

G10 and FR4 sheets are machined into washers, spacers, standoffs, and sleeves using carbide or diamond tooling. The abrasive glass content wears standard high-speed steel tools quickly, so tooling selection directly affects edge quality and tolerance holding.

• CNC routing and milling: Standard for flat washers and complex profiles. Multi-pass cuts reduce delamination at the edges.
• Punching: Suitable for high volumes of simple round washers in thinner sheets. Punch-and-die clearance must match the sheet thickness to avoid cracking.
• Drilling and reaming: Used for tight-tolerance holes. Back-up plates and controlled feed rates reduce breakout on the exit side.
• Tolerances: Typical commercial tolerances are ±0.1 mm to ±0.3 mm for ID/OD, depending on size and quantity. Tighter tolerances require secondary finishing and inspection.

IncomePultrusion machines G10 and FR4 washers and spacers to customer drawings. Provide the grade, thickness, quantity, and any critical tolerances or inspection requirements when requesting a quote.

When to Choose an FR4 Washer

FR4 is the safer choice when any of the following apply:

• The drawing or specification calls for a flame-retardant material.
• The assembly is installed in electrical panels, switchgear, or control cabinets where fire safety standards apply.
• The end customer requires NEMA FR4 or an equivalent fire-rated laminate.
• The part may be exposed to elevated temperatures and a higher glass-transition material is specified.

When to Choose a G10 Washer

G10 is appropriate when flame retardancy is not specified and the priority is cost, availability, or general electrical isolation:

• General-purpose electrical isolation between bolts and frames.
• Custom spacers, standoffs, and gaskets where no fire rating is required.
• Prototypes and low-volume production where material lead time matters.
• Applications where the natural color and appearance of G10 are acceptable.

Typical Applications

G10 and FR4 machined parts are used wherever a strong, non-conductive spacer or washer is needed in a dry or sheltered environment.

• Electrical panels and switchgear: Busbar isolation washers, mounting spacers, and barrier supports.
• Transformers and distribution equipment: Insulating pads and terminal washers that separate conductors from grounded frames.
• Electronics enclosures: Standoffs, insulating sleeves, and gaskets for sensitive assemblies.
• Rail and transit: Non-metallic spacers where flammability standards require FR4.
• Industrial machinery: Custom shims and wear pads where electrical isolation or low magnetic signature is required.

FR4/G10 vs Pultruded FRP Washers

Both material groups contain glass fiber and resin, but their manufacturing methods and typical uses differ.

• FR4/G10 washers are machined from flat laminate sheets. They are chosen for electrical isolation, dimensional accuracy, and flame-retardant requirements. They are not typically selected for long-term immersion in aggressive chemicals.
• Pultruded FRP washers are produced by pulling continuous fibers through a resin bath and die. They are optimized for corrosion resistance and are used with FRP bolts and nuts in chemical plants, water treatment facilities, and marine structures.

For electrical isolation in a dry cabinet, G10 or FR4 is usually the better fit. For corrosion resistance in a wet chemical environment, a pultruded FRP washer from the FRP washers guide or the FRP washer product page is more appropriate.

Ordering Custom Washers and Parts

IncomePultrusion supplies CNC-machined G10 and FR4 washers, spacers, standoffs, and sleeves to drawing. Standard lead time is typically 1 to 3 weeks depending on quantity, thickness, and tolerance requirements.

To request a quote, include the following information:

• Material grade (G10 or FR4)
• Sheet thickness and finished part thickness
• Inside diameter, outside diameter, and quantity
• Any critical tolerances or surface requirements
• Application temperature, flame, or electrical requirements
• Inspection or documentation requirements (datasheet, certificate, batch test)

For dedicated laminate washer specifications, see the G10 & FR4 washers page. For application advice or a formal quotation, use the quote request page.

Frequently Asked Questions

What is G10 material?

G10 is a NEMA-grade epoxy fiberglass laminate made from woven glass fabric and epoxy resin. It is strong, dimensionally stable, and electrically insulating in dry conditions.

Is G10 the same as Garolite?

Garolite is a brand name for glass-reinforced epoxy laminates, including G10. Not all G10 is sold under the Garolite brand, and properties vary by supplier.

FR4 vs G10 — which is better for insulating washers?

For general electrical isolation, both perform similarly. Choose FR4 when a flame-retardant rating is required; choose G10 when it is not, to reduce cost.

Can both be CNC machined?

Yes. Both G10 and FR4 machine cleanly with carbide or diamond tooling. CNC machining is the standard method for producing custom washers, spacers, and standoffs.

Is there a big price difference?

FR4 is usually slightly more expensive than G10 because of the flame-retardant additive. The actual difference depends on sheet thickness, part size, quantity, and tolerance.

Request a Quote for G10 or FR4 Washers

Not sure whether G10 or FR4 is right for the application? Submit the drawing, operating temperature, and any flame or electrical requirements through the quote request page. IncomePultrusion machines custom G10 and FR4 washers, spacers, and sleeves to drawing.