A small 4 layer rigid-flex PCB made by Storm Circuit some days ago.
Rigid-Flex printed circuit boards are PCB boards using a combination of flexible and rigid board technologies.Many PCB designers do not know how to design the rigid-flex PCB ,or do not know what information you need to provide to PCB suppliers. We have a rigid-flex PCB design guide here,it may help you. PCB designers have to provide us the rigid part thickness and the flex part thickness, if there is a stackup to show each layer /PP thickness, that helps us much .
We made a lot of double sided rigid-flex PCB ,rigid part is usually 1.6mm, and flex part is 0.15-0.2mm.
Here is a 4 layer rigid-flex PCB. Flex part is in inner layers,thickness 0.12mm. rigid part 1.0mm.