Rigid Flex is more of a construction technique than an actual single material. As its name implies, "Rigid-Flex" is a composite of two different materials, one flexible, (such as Pyralux) and the other rigid (FR-4).
The applications for this type of board are practically unlimited, but its functionalities are especially useful for any application that requires connection to moving or bending parts and also requires a stable platform for components. Example applications include video cameras, laptops, or cellular phones. These consumer products have moving parts that bend of fold but are still connected to solid platform.
Rigid Flex is more of a construction technique than an actual single material. As its name implies, "Rigid-Flex" is a composite of two different materials, one flexible, (such as Pyralux) and the other rigid (FR-4). 
