FR4 is a flame-retardant glass-reinforced epoxy laminate defined by NEMA standard LI-1 and classified as Grade FR-4. It belongs to the glass epoxy family — thermoset composites manufactured from woven fiberglass cloth impregnated with epoxy resin and cured under heat and pressure into rigid sheet, rod, and tube stock. The combination of woven glass reinforcement and epoxy binder makes FR4 one of the most widely specified fr4 material grades in electrical insulation and structural applications.
FR4 delivers 65,000 psi tensile strength, 60,000 psi flexural strength, and 38,000 psi compressive strength with a Rockwell M115 hardness. Water absorption over 24 hours is only 0.10%, giving FR4 sheet excellent dimensional stability in humid environments. Maximum continuous service temperature is 280°F (140°C). These properties make FR4 laminate an industry default for printed circuit boards, transformer components, electrical enclosures, and precision-machined insulating parts.
Standards. FR4 meets NEMA LI-1 Grade FR-4 requirements and carries a UL 94 V-0 flammability rating — self-extinguishing with vertical flame exposure. This fr4 plastic grade is also compliant with ASTM D709 test methods for laminated thermosetting materials.
Related grades. When flame retardance is not required, G-10 glass epoxy offers a similar property profile at a cost advantage. For higher operating temperatures, step up to G-11 or FR-5, both of which extend continuous service to 180°C while maintaining flame-retardant performance. Ready Plastics stocks FR4 in sheet and rod forms — contact us or request a datasheet for available sizes.
