Epoxy FR4
Flame-retardant grade
ASTM D1763 · GB GB/T 13657 · ISO 3673-1
FR4 = fR-4 / G-10
Pick for PCB substrates, insulating plates and machined electrical parts needing high flexural strength plus V-0 rating.
Values for the FR4 condition
Other Epoxy grades and fills
Epoxy is listed in 10 conditions; see the grade overview at Epoxy.
Compare all 10 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Syntactic foam / microballoon-filled low-density grade | Buoyancy modules, core materials and lightweight tooling fills where compressive strength per density rules. | — | 20 | 1.2 | 80 Shore D |
ESD / electrically conductive | Conductive adhesives, EMI/grounding bondlines and static-dissipative tooling surfaces. | — | 30 | 0.5 | 90 Shore D |
Thermally conductive | Gap fillers and heat-sink potting where 1–3 W/m·K is needed while keeping electrical insulation. | — | 40 | 0.8 | 90 Shore D |
Toughened / impact-modified | Structural adhesives and crash-tolerant bondlines — 3–5× fracture toughness at the cost of Tg and modulus. | — | 45 | 9 | 78 Shore D |
Mineral / silica filled encapsulation grade | Silica-filled potting/encapsulation compound — low CTE and shrinkage for electronics, transformers and semiconductor molding. | — | 55 | 1 | — |
FR | Brominated or phosphorus/ATH flame-retarded formulation for electrical enclosures, busbar and rail applications. | — | 55 | 2 | 88 Shore D |
High-Tg novolac / anhydride cured heat-resistant grade | For tooling, aerospace prepreg and under-hood parts needing service to ~180–200 °C; more brittle and needs high-temperature post-cure. | — | 70 | 1.8 | — |
30 % short glass fiber reinforced epoxy molding compound | Choose for stiff, dimensionally stable molded parts (encapsulation, electrical housings) where CTE must be halved versus neat resin. | — | 110 | 1.5 | — |
FR4This page FR-4 / G-10 | Pick for PCB substrates, insulating plates and machined electrical parts needing high flexural strength plus V-0 rating. | — | 310 | — | — |
Carbon fiber / epoxy composite | Use when epoxy acts as the matrix of a structural CFRP laminate — highest specific stiffness, near-zero axial CTE. | — | 1,800 | 1.4 | — |
What is Epoxy FR4?
Epoxy FR4 is Epoxy in the FR4 grade — pick for PCB substrates, insulating plates and machined electrical parts needing high flexural strength plus V-0 rating. Epoxy FR4 has a tensile strength of 310 MPa (45 ksi), stronger than 100% of polymer grades. Elongation at break is 4% and the elastic modulus is 22 GPa (3.19 Msi). Epoxy FR4 has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is 135°C (275 °F).
Advantages
- Stiff — 22 GPa (3.19 Msi), better than 100% of polymer grades
- Low, predictable mold shrinkage — 0.2%, better than 94% of polymer grades
- Conducts heat well — 0.35 W/m·K (0.202 BTU/hr·ft·°F), better than 91% of polymer grades
- Polishes to a fine finish — 75/100, better than 86% of polymer grades
Limitations
- Difficult to weld — 0/100, worse than 98% of polymer grades
- Low fracture toughness — 0.6 MPa·√m (0.546 ksi·√in), worse than 96% of polymer grades
- Heavy — 1.85 g/cm³ (0.0668 lb/in³), worse than 96% of polymer grades
- Limited formability — 5/100, worse than 95% of polymer grades
- Difficult to machine — 30/100, worse than 87% of polymer grades
Epoxy FR4 properties
Typical room-temperature values for Epoxy FR4; 17 are specific to this condition. Other listed values are Epoxy reference data and may not represent this condition. Bars are the position among polymer grades.
Physical6
Epoxy FR4 has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is 135°C (275 °F).
Mechanical15
Epoxy FR4 has a tensile strength of 310 MPa (45 ksi), stronger than 100% of polymer grades. Elongation at break is 4% and the elastic modulus is 22 GPa (3.19 Msi).
Thermal10
Epoxy FR4 is rated for continuous service to 130°C (266 °F). It conducts heat at 0.35 W/m·K (0.202 BTU/hr·ft·°F), better than 91% of polymer grades. Thermal expansion is 15 µm/m·K (8.33 µin/in·°F).
Electrical7
Epoxy FR4 is an electrical insulator with a dielectric strength of 20 kV/mm (508 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (82/100), better than 56% of polymer grades. UV resistance is poor.
Sustainability4
Producing a kilogram of Epoxy FR4 takes about 137 MJ of energy and emits 6.6 kg of CO₂ — more than 80% of polymer grades. Typical recycled content is 0%.
Manufacturability6
Epoxy FR4's machinability is poor (30/100, worse than 87% of polymer grades); weldability not recommended (0/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Epoxy FR4
Is Epoxy easy to machine?
Machines cleanly with sharp carbide (PCD for filled/laminate grades) at high speed, light feed and no coolant heat build-up; filled and glass-cloth grades are highly abrasive and the dust requires extraction.
Can Epoxy be welded?
Thermoset — cannot be welded or re-melted; joints are made by secondary epoxy bonding with abraded, solvent-cleaned surfaces.
Can Epoxy be formed, bent or molded?
Processed by casting, potting, RTM/infusion, prepreg lay-up, filament winding or transfer/compression molding; degas the mix, respect pot life, and post-cure (typically 80–180 °C) to develop full Tg.
What surface finishes work on Epoxy?
Sands and polishes to a high gloss; accepts paint and primers readily after abrasion; needs UV-blocking topcoat or clearcoat for outdoor service because aromatic epoxies yellow and chalk.
Epoxy chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| bisphenol-A diglycidyl ether (DGEBA) resE-51/E-44 type; novolac or cycloaliphatic epoxies substitute in HT/clear grades | 45 – 75 | 60 |
| amine or anhydride hardenerpolyamine, polyamide, DDS/DDM or MTHPA anhydride; stoichiometry set by EEW | 8 – 40 | 25 |
| reactive diluent / flexibilizere.g. BGE, C12-14 glycidyl ether, CTBN | 0 – 15 | 5 |
| mineral or glass fillersilica, alumina, glass fiber/cloth depending on variant | 0 – 70 | 0 |
| accelerator / additivesimidazole, BDMA, defoamer, pigment, FR package | 0 – 3 | 1 |
Epoxy FR4 — frequently asked
What is Epoxy FR4 used for?
Epoxy FR4 is typically used for composite laminates, structural adhesives, potting/encapsulation and tooling and molds. In short: baseline composite matrix; strongest structural adhesive resin; wide filled-grade range.
What is the tensile strength of Epoxy FR4?
Epoxy FR4 has a typical tensile strength of 310 MPa (45 ksi) — stronger than 100% of polymer grades. Strength varies by condition: see the 10 listed tempers.
Is Epoxy FR4 easy to machine?
Not especially — machinability is rated poor (30/100, worse than 87% of polymer grades). Machines cleanly with sharp carbide (PCD for filled/laminate grades) at high speed, light feed and no coolant heat build-up; filled and glass-cloth grades are highly abrasive and the dust requires extraction.
Can Epoxy FR4 be welded?
Not readily — weldability is rated not recommended (0/100). Thermoset — cannot be welded or re-melted; joints are made by secondary epoxy bonding with abraded, solvent-cleaned surfaces.
What surface finishes work on Epoxy FR4?
Sands and polishes to a high gloss; accepts paint and primers readily after abrasion; needs UV-blocking topcoat or clearcoat for outdoor service because aromatic epoxies yellow and chalk.
Can Epoxy FR4 be formed, bent or molded?
Processed by casting, potting, RTM/infusion, prepreg lay-up, filament winding or transfer/compression molding; degas the mix, respect pot life, and post-cure (typically 80–180 °C) to develop full Tg.
What is the maximum service temperature of Epoxy FR4?
Epoxy FR4 is rated for continuous use to about 130°C (266 °F), and briefly to 180°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- Engineered Materials Handbook Vol. 2 — Engineering Plastics — ASM International (1988)
- Engineered Materials Handbook Vol. 1 — Composites — ASM International (1987)
- ASTM D1763 — Standard Specification for Epoxy Resins — ASTM (2019)
- GB/T 13657 — Bisphenol-A epoxy resin — SAC (2011)
- IEC 61249 / NEMA LI-1 (FR-4, G-10 laminates) — IEC / NEMA (2020)
- Araldite / Aradur casting and adhesive system datasheets — Huntsman Advanced Materials (2023)
- EPON / EPIKURE resin technical data — Hexion (Westlake Epoxy) (2022)
- CES EduPack polymer records — epoxy (thermoset) — Ansys Granta (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.