Abstract: A method and device for fabricating posts made of concrete having a polygonal cross-section includes the steps of providing and opening an integral liner, applying backing panels to the liner, holding the panels together with a hooping means, and pouring and hardening concrete in the integral liner. The liner is collapsible and preformed to open in the shape of a right prism with an internal section identical to that of the post to be manufactured. Backing panels made of cardboard or plastic material support the external faces of the liner and entirely cover the external faces of the liner. At least one of the backing panels is adhered to an external face of the liner. A hooping means holds the liner and the backing panels assembled in mutual contact during the use of the device.