Flexible PCBs are created on the basis of a thin material that is highly flexible due to the use of polyimide film or polyethylene terephthalate. Thanks to the high flexibility, PCBs can be bent without breaking or losing strength.
That's why they can be used for three-dimensional installation. They are able to bend the contours of electronic device blocks.
Flexible-rigid PCB is a hybrid that is designed with both rigid and flexible parts. Parts can be combined in different ways.
Either rigid and flexible layers go separately, or each layer has both rigid and flexible parts.
It allows to solder components to the rigid part of PCB, when a flexible PCB transmits a signal where a rigid one would not cope due to its weak flexibility or thicker base. Such PCB has the advantages of both flexible classic PCBs and rigid ones.
In comparison with conventional rigid PCBs, such structures are smaller in size and weight, and the connections on them live longer due to reliability and resistance to the external environment. Such PCBs allow to completely abandon connectors.