Shop for FR-4 Glass Epoxy rods. FR-4 glass epoxy rod is a composite material that consists of glass fabric, electrical grade epoxy resin. The material is extremely strong and stiff, has a low coefficient of thermal expansion, and outstanding electrical properties. Have machined into fabricated parts. Stocked materials typically ship in 2-5 business days. Can’t find what you need? Get a quote or learn more about G10/FR-4 glass epoxy.