Plastic shoe shank
Shoe shank can be made of plastic, and sometimes from fiberglass (fiberglass). A modern plastic shoe shank significantly lightens the weight of the shoe, but is not inferior in strength to the metal one. Also that a plastic or fiberglass shoe shank is guaranteed to not cause problems when passing control at the airport, but a metal one can “excite” devices and cause you little troubles.
Plastic shoe shank CAMB 1