Building cylinders, for use in machines for the layer-by-layer production of 3D objects by sintering or melting powdered material by a high-energy beam, and having a main body and a piston part movable on an inner side of the main body along a cylindrical axis, are disclosed. The piston part has a base element for the growth of a 3D object, and a powder seal bearing against the inner side of the main body for sealing the powdered material. The piston part has a seal carrier on which the powder seal is mounted, and an insulator, e.g., a circumferential insulation ring, mounted on the seal carrier. The base element is mounted on the insulator and is arranged at a distance from the seal carrier and from the powder seal.