Product A flexible PCB, often called a flex circuit or FPC, is a printed circuit board that is designed to be bent, twisted, and folded without losing its electrical integrity. Unlike traditional rigid PCBs made from fiberglass, flex PCBs use a flexible plastic substrate, most commonly polyimide (PI). This unique characteristic makes them invaluable in a wide range of products, especially where space is at a premium or where the device needs to conform to a specific shape.