Main material composition of FPC: Substrate & Coverlay (similar to solder mask ). And the substrate is mainly composed of PI / PET + adhensive + copper.

PS:

PI— A polyimide insulating resin material, characterized by high temperature resistance, good bending performance and good reliability of the products produced, which is the major material of FPC.

PET— A polyester insulating resin material whose characteristics is exactly opposite of PI. And it is rarely used in general FPC factory.

Adhensive & Copper—Copper is an electrical conductor. The role of adhensive that is to bond copper to PI or PET. The substrate that is finally made into FPC, which is equivalent to the substrate of PCB.

Coverlay (a protective film like solder mask)— A surface insulating layer of FPC.