Can refer to a person or thing that appears stiff or unnatural.
El cartón acartonado del envase no se puede reciclar adecuadamente.
The cardboard-like carton of the package cannot be recycled properly.
El cartón de la caja era tan acartonado que se rompió al intentar abrirla.
The cardboard of the box was so stiff that it broke when trying to open it.