A method for pinning the edges of an extruded polymeric mass , comprising the following steps: - an extrusion step in which the polymeric mass is extruded from an extrusion die ; at least two pre-cooling steps, wherein - two areas are defined in the extruded polymeric mass along each of the external edges of the mass itself, respectively having a width equal to (a) and (b) (15' and 15) and a length equal to the length of the extruded mass , wherein the area having a width (a) , having a variable width, is arranged flush with the edge of the extruded mass and the area having a width (b) is adjacent to the area having a width (a) , internally with respect to the edge of the extruded mass , and - a third area having a width equal to (c), , and a length equal to the length of the extruded mass , adjacent to the area having a width (b) , internally with respect to the edge of the extruded mass ; - in the first pre-cooling step, the area having a width (c) of the polymeric mass is pre-cooled by the action of an air flow, before the extruded mass is cast and comes into contact with the surface of a rotating cylinder positioned at a distance d from the extrusion die ; - in the second subsequent pre-cooling step, the area having a width (b) is pre-cooled by means of a second flow of air, before the extruded mass is cast and comes into contact with the surface of a rotating cylinder positioned at a distance d from the extrusion die ; said method being characterized in that it comprises at least two electrostatic charging steps of the extruded polymeric mass , wherein - in the first electrostatic charging step, the area having a width (b) , pre-cooled in the previous step, is electrostatically charged to favour its adhesion to the surface of the cylinder and ensure the correct heat exchange between the two elements; - in the second electrostatic charging step, the area having a width (a) , arranged flush with the edges of the extruded mass , externally with respect to the area having a width (b) , treated in the previous step, is electrostatically charged. - an extrusion step in which the polymeric mass is extruded from an extrusion die ; at least two pre-cooling steps, wherein - two areas are defined in the extruded polymeric mass along each of the external edges of the mass itself, respectively having a width equal to (a) and (b) (15' and 15) and a length equal to the length of the extruded mass , wherein the area having a width (a) , having a variable width, is arranged flush with the edge of the extruded mass and the area having a width (b) is adjacent to the area having a width (a) , internally with respect to the edge of the extruded mass , and - a third area having a width equal to (c), , and a length equal to the length of the extruded mass , adjacent to the area having a width (b) , internally with respect to the edge of the extruded mass ; - in the first pre-cooling step, the area having a width (c) of the polymeric mass is pre-cooled by the action of an air flow, before the extruded mass is cast and comes into contact with the surface of a rotating cylinder positioned at a distance d from the extrusion die ; - in the second subsequent pre-cooling step, the area having a width (b) is pre-cooled by means of a second flow of air, before the extruded mass is cast and comes into contact with the surface of a rotating cylinder positioned at a distance d from the extrusion die ; - in the first electrostatic charging step, the area having a width (b) , pre-cooled in the previous step, is electrostatically charged to favour its adhesion to the surface of the cylinder and ensure the correct heat exchange between the two elements; - in the second electrostatic charging step, the area having a width (a) , arranged flush with the edges of the extruded mass , externally with respect to the area having a width (b) , treated in the previous step, is electrostatically charged. <EOS>