Abstract: The present disclosure relates to a permanent plastic formwork system formed by two parallel surfaces, namely an outer surface and an inner surface, comprising a plurality of flat or longitudinally curved, hollow plastic slats obtained by means of extrusion, provided internally with a rebar mesh providing them with rigidity and joined longitudinally by means of tongued-and-grooved ends with separators existing between the two surfaces. The separators are provided with a threaded area and an inclined appendage for securing the rebar mesh located between the surfaces. The slats are secured to the ground using U-shaped parts containing a threaded rod that can be used to clamp and fix the same. In addition, in closed structures, reinforced internal elements can be incorporated diametrically, such as metal bars with flat surfaces at their ends enabling the same to be secured to the above-mentioned inner surface.