Material guide
G10 vs FR-4: What's the Difference?
G10 and FR-4 are nearly identical glass-epoxy laminates. The difference is flame retardancy. Here's how they compare, where G11 and phenolic laminates fit, and machining tips for glass-epoxy.
FR-4 is G10 with a flame retardant added (rated UL94 V-0). Mechanically and electrically they're nearly the same. Choose FR-4 when a flame rating is required, such as circuit boards and electrical equipment. G10 is fine when it isn't. Many suppliers sell dual-certified G10/FR-4 sheet, which covers both.
The short version
G10 and FR-4 are NEMA grades of laminate made from woven glass cloth and epoxy resin. They share the same strength, stiffness, low moisture absorption and excellent electrical insulation. The difference is the resin: FR-4's contains a flame retardant, so it self-extinguishes and carries a UL94 V-0 rating. In stock shapes, a lot of what's sold today is dual-rated.
| G10 | FR-4 | G11 / FR-5 | |
|---|---|---|---|
| Reinforcement | Woven glass + epoxy | Woven glass + epoxy | Woven glass + high-temp epoxy |
| Flame retardant | No | Yes (UL94 V-0) | G11 no, FR-5 yes |
| Max operating temp (typical) | ~266°F (130°C) | ~266–284°F (130–140°C) | ~302°F (150°C) and up |
| Strength and stiffness | Very high | Very high | High, better retained when hot |
| Electrical insulation | Excellent | Excellent | Excellent |
| Moisture absorption | Very low | Very low | Very low |
| Relative cost | $$ | $$ | $$$ |
Typical values; properties vary by manufacturer and thickness. Confirm with the datasheet for your grade.
Where each is used
- FR-4: printed circuit boards, electrical panels and insulators where a flame rating is required.
- G10: insulating washers, spacers, standoffs, fixtures, test jigs, wear plates and knife handle scales.
- G11 / FR-5: parts that must keep their strength at higher temperatures, like motor and transformer insulation.
How phenolic laminates compare
Paper, canvas and linen phenolics (grades like XX, CE and LE) are the lower-cost cousins. They machine more easily and are kinder to tooling, but they're weaker, absorb more moisture and aren't as good electrically as glass-epoxy. Canvas and linen phenolics are popular for wear parts, gears and fixtures; G10/FR-4 is the step up when strength, insulation or stability matters more.
Machining glass-epoxy
- Use carbide or diamond tooling; glass is very abrasive.
- Control dust with extraction or wet machining, and use respiratory protection.
- Support edges and use sharp tools to avoid chipping, fraying and delamination.
- Expect slightly looser tolerances on edges and holes than with unfilled plastics.
Find CNC machine shops and CNC routing shops that list G-10 and phenolics below.
Tip from the counter: if a print says G10 and you have FR-4 (or dual-rated G10/FR-4) on the shelf, it almost always works. The reverse isn't true when a flame rating is called out.
Common questions
What material is equivalent to FR-4?
G10 is the closest equivalent; it's the same woven glass and epoxy laminate without the flame-retardant additive. Many suppliers sell sheet certified to both grades, often labeled G10/FR-4. For higher temperatures, G11 and FR-5 are the step-up grades. Garolite is a trade name commonly used for these laminates.
Is G10 just fiberglass?
It's fiberglass cloth bonded with epoxy resin, pressed into sheets, rods and tubes under heat and pressure. That makes it much stronger, stiffer and more stable than the chopped-strand fiberglass in boats and panels, with excellent electrical insulation.
Is G10 brittle?
G10 is very strong and stiff, but it isn't tough the way metals or nylon are. It can chip or delaminate at edges and corners, and it cracks rather than bends when overloaded. Machined edges and holes should be sharp and supported to avoid fraying or chipping.
Is G10 a good thermal insulator?
Yes. Like most plastics and composites it conducts heat poorly, and it's also an excellent electrical insulator with low moisture absorption. That's why it's used for insulating washers, standoffs, terminal boards and thermal breaks.
Is it safe to machine G10?
It can be, with precautions. Machining glass-epoxy creates fine abrasive glass dust that irritates skin and lungs. Shops use dust extraction or wet machining and respiratory protection, and carbide or diamond tooling because the glass wears tools quickly.
Values in this guide are typical figures for common unfilled grades, for general comparison only. Properties vary by manufacturer, grade, filler, and shape. Before you specify, buy or machine a material for an application, check the manufacturer's datasheet and the material certifications for the exact grade you're getting, and confirm suitability with your supplier.
Who stocks and machines it
Distributors that stock these materials and shops that machine or fabricate them, from the Stock & Shape directory.
Phenolic/G-10
- Calsak Plastics – Atlanta Lawrenceville, GA
- Emco Industrial Plastics Cedar Grove, NJ
- Interstate Advanced Materials – Portland Portland, OR
- Piedmont Plastics – Bay Area Union City, CA
- Definitive Solutions & Technologies Auburn, WA
- J & N Metal Products Brazil, IN
- Metal Working Technology Cornwall Bridge, CT
- MG Machine Belton, MO