Flexible circuits have an advantage over Rigid FR4 PCB in that they can bend, fold, twist and wrap in extremely tight areas, over multiple times. This provides designers freedom to locate parts together, that would otherwise not fit, and thereby reduce the packaging size of their products.
The most widely used Flexible Circuits & flex printed circuits (FPC) material today is manufactured by Dupont Corporation and is called "Kapton". This polyimide film based material is resistant to heat, has dimensional stability and a low dielectric constant of 3.6. The follows are basic Kapton materials: