A method of molding a collapsible, foam plastic container; the container comprising a bottom wall, and four lateral walls (7, 8) facing each other in pairs, and being movable between a work configuration, in which the lateral walls (7, 8) are substantially perpendicular to one another and to the bottom wall, and a flat rest configuration, in which the lateral walls (7, 8) are parallel to one another and to the bottom wall; the method comprising the steps of: preparing a mold comprising a first half-mold and a second half-mold movable with respect to each other to and from a closed molding position, in which the two half-molds (3, 4) define between them a molding chamber negatively reproducing the shape of the container in the work configuration; and performing a molding cycle comprising a step of closing the two half-molds (3, 4), a molding step, and a step of opening the half-molds (3, 4) and removing the molded container; wherein the molding step comprises a sub-step of forming, for each lateral wall (7; 8), a respective hinge (14; 15) designed to allow the lateral wall (7; 8) to rotate with respect to the bottom wall; said sub-step of forming each hinge (14; 15) being performed by a forming device comprising, for each hinge (14; 15) to be formed, a parting member activated to move between a rest position outside the molding chamber, and a work position in which it penetrates the molding chamber at the hinge (14; 15) to be formed; characterized by a compression member (53; 61) located on the opposite side of the molding chamber to the parting member, and which is activated to move between a rest position outside the molding chamber, and a work position in which it compresses a quantity of plastic material towards the parting member, and cooperates with the parting member to form, on the lateral wall (7; 8), a small-section, higher-density portion defining the respective hinge (14; 15); and wherein, when filling the molding chamber with the plastic material, a given quantity of plastic material is fed into chambers (56, 64) communicating with the molding chamber and extending at respective hinges (14, 15) to be formed; each compression member (53; 61) being mounted movably inside a respective said chamber (56, 64), and being moved, at said forming sub-step, inside the chamber (56, 64) to push the material in the chamber (56, 64) into the molding chamber and towards the respective parting member. preparing a mold comprising a first half-mold and a second half-mold movable with respect to each other to and from a closed molding position, in which the two half-molds (3, 4) define between them a molding chamber negatively reproducing the shape of the container in the work configuration; and performing a molding cycle comprising a step of closing the two half-molds (3, 4), a molding step, and a step of opening the half-molds (3, 4) and removing the molded container; wherein the molding step comprises a sub-step of forming, for each lateral wall (7; 8), a respective hinge (14; 15) designed to allow the lateral wall (7; 8) to rotate with respect to the bottom wall; said sub-step of forming each hinge (14; 15) being performed by a forming device comprising, for each hinge (14; 15) to be formed, a parting member activated to move between a rest position outside the molding chamber, and a work position in which it penetrates the molding chamber at the hinge (14; 15) to be formed; characterized by a compression member (53; 61) located on the opposite side of the molding chamber to the parting member, and which is activated to move between a rest position outside the molding chamber, and a work position in which it compresses a quantity of plastic material towards the parting member, and cooperates with the parting member to form, on the lateral wall (7; 8), a small-section, higher-density portion defining the respective hinge (14; 15); and wherein, when filling the molding chamber with the plastic material, a given quantity of plastic material is fed into chambers (56, 64) communicating with the molding chamber and extending at respective hinges (14, 15) to be formed; each compression member (53; 61) being mounted movably inside a respective said chamber (56, 64), and being moved, at said forming sub-step, inside the chamber (56, 64) to push the material in the chamber (56, 64) into the molding chamber and towards the respective parting member.