Flex PCB and Rigid Flex PCB

Flex PCB
Flex circuits, also known as Flexible PCB, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film.

Rigid flex PCB
Rigid flex circuits are a hybrid construction flex circuit consisting of rigid and flexible substrates which are laminated together into a single structure.Rigid flex also know as Rigid flex PCB. Rigid-flex circuits should not be confused with rigidized flex constructions, which are simply flex circuits to which a stiffener is attached to support the weight of the electronic components locally. A rigidized or stiffened flex circuit can have one or more conductor layers. Thus while the two terms may sound similar, they represent products that are quite different.