G-10 / FR-4
A glass-epoxy laminate for insulating parts
Typical values for the temper in the title
G-10 is a laminate of woven glass cloth layers in epoxy resin, and FR-4 is the same material in a flame-retardant version. It is strong and stiff, an excellent electrical insulator, dimensionally stable and absorbs very little water (under 0.10%), so it is one of the most common shop materials for machined insulating parts.
It is used for electrical insulators and barriers, mechanical parts that need insulation, jigs and fixtures, and as a printed circuit board substrate. For higher heat (about 170–180 °C) there are G-11 and FR-5, with high-temperature epoxy.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | ≈275 MPa (lengthwise) | |
| Density ρ | 1.85 g/cm³ | |
| Max service temperature | ≈130–140°C (mechanical) | |
| Machinability | Carbide/diamond tools — glass dust | relative rating in the site database |
Structure: fiber and matrix
| Feature | Value | Meaning |
|---|---|---|
| Reinforcement | woven glass cloth | strength and stability |
| Resin | epoxy (in FR-4: flame retardant) | insulation and moisture resistance |
| Directionality | lengthwise slightly stronger than crosswise | tension about 276 / 241 MPa |
Typical values per producer data.
Constructions and versions
In laminates the choice is by reinforcement (glass cloth, paper, cotton) and resin. Each NEMA grade is also defined in a separate MIL-I-24768 slash sheet.
| Version | Properties | When to choose it |
|---|---|---|
| G-10 (MIL-I-24768/2, GEE) | basic glass-epoxy laminate | insulating parts |
| FR-4 (MIL-I-24768/27, GEE-F) | flame retardant | circuits and electrical components |
| G-11 / FR-5 | high-temperature epoxy (about 170–180 °C) | hot parts |
Applications
- Electrical insulators and barriers
- Insulating mechanical parts
- Jigs and fixtures
- Printed circuit board substrates
- Light structural panels
Fabrication
Machining
Machines well, but the glass is abrasive to tools. Carbide or diamond tools, high speed and low feed.
Safety
The glass dust irritates skin and lungs. Work with extraction and protection, preferably wet.
Directionality
Strength through the thickness (between plies) is low. Do not load a part so that the plies peel apart.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| Phenolic Laminate | 65–140 MPa (by grade) | No — mechanical joining | phenolic laminate: cheaper, easy to machine, absorbs moisture · material page |
| GFRP Woven Glass | 350 MPa | Not possible | woven glass composite: for large parts · material page |
| PEI (Ultem) | 105 MPa | Ultrasonic | PEI: an insulating engineering plastic, for heat · material page |
Common mistakes
Machining dry without extraction
Glass dust is an irritant.
Loading through the thickness
The plies may separate.
Using it above about 130–140 °C under load
For higher heat, G-11 or FR-5.
Equivalents, standards and supply
| NEMA | G-10 / FR-4 |
|---|---|
| MIL | MIL-I-24768/2 (GEE), /27 (GEE-F) |
| Standards | NEMA LI 1 / MIL-I-24768/2 (G-10) / MIL-I-24768/27 (FR-4) |
| Forms | sheet · rod · tube |
| Producers | Isola · Acculam · Röchling |
Learn more
Values are typical and for comparison only. In composites, properties depend strongly on fiber direction, fiber content, layup and process. For design, rely on data for the specific laminate and tests. The standards mentioned are mainly test methods (ASTM D3039, D3410, D2344 and others). Sources: producer data and the METAL HUB materials database.
Updated: October 31, 2026