G-3 glass phenolic is a woven-glass-fabric/phenolic-resin thermoset laminate defined by NEMA LI-1 Grade G-3. It belongs to the glass phenolic family — composites manufactured by impregnating woven glass cloth with phenolic resin, then curing under heat and pressure. Compared to paper-based phenolics, the woven glass reinforcement gives G-3 g3 material significantly improved tensile strength and dimensional stability, making it a practical step up for applications that demand more mechanical load-bearing capability alongside dependable electrical insulation.
G-3 delivers 76,000 psi tensile strength, 55,000 psi flexural strength, and 18,000 psi shear strength with a Rockwell M110 hardness. Water absorption over 24 hours is 2.0% — higher than epoxy-based grades but acceptable for many dry or low-humidity environments. Maximum continuous service temperature is 280°F (140°C). These properties suit G-3 for switchgear panels, terminal boards, electrical enclosures, spacers, and structural insulating components where glass-reinforced phenolic performance is specified.
Standards. G-3 meets NEMA LI-1 Grade G-3 and carries a UL 94HB flammability rating. Test methods follow ASTM D709. The phenolic resin system provides inherent rigidity and good chemical resistance, though moisture absorption is higher than glass epoxy alternatives.
Related materials. When moisture resistance and higher dielectric strength are critical, glass epoxy grades such as G-10 or FR-4 provide lower water absorption and stronger electrical performance. For cost-sensitive applications with lighter mechanical demands, paper phenolic grades are available in the broader glass phenolic family at Ready Plastics. Contact us for available sheet and rod dimensions.
