FR-4 is a code of fire-resistant material grade, which means that the resin material must be able to extinguish itself after burning. It is not a name of material, but a material grade. Therefore, there are many kinds of FR-4 grade materials used in general circuit boards, but most of them are combined materials that consists of Epoxy resin with Tera function, filler and fiberglass composites. Its main technical features and application include stable electrical insulation performance, good flatness, smooth surface, no pit, standard thickness tolerance. Which is suitable for high-performance electronic insulation products, such as FPC reinforcing plate, PCB drilling pad, fiberglass meson, potentiometer carbon film printed fiberglass board, precision star gear (wafer grinding), precision test plate, electrical (Electrical) equipment Insulation strip partition, insulation pad, transformer insulation board, motor insulation parts, grinding gear, electronic switch insulation board, etc.

FR-4 is the base plate used for PCB, which is a kind of sheet material. According to different reinforcement materials, sheet metal is mainly classified into the following four categories:
1) FR-4: glass cloth base plate
2) FR-1, FR-2, etc.: paper base plate
3) CEM series: composite base plate
4) special material base plate (ceramic, metal base, etc.)— FR-4 is a plate laminated product that made of special electronic cloth soaked with epoxy phenolic resin and other materials by high temperature, high pressure and hot pressing.

Features of FR-4: High mechanical and dielectric properties, good heat resistance and moisture resistance, and good machinability.
Application of FR-4: Used as insulation structural parts in motor and electrical equipment, including various types of switches, FPC reinforcing electrical insulation, carbon film printed circuit board, computer drilling pad, mold and fixture (PCB test stand), and can be used in humid environment and transformer oil.