A method of formfree printing a three-dimensional object in layers with at least one printing material includes outputting printing material in at least one printing material string in string-shape via at least one printing head; receiving, via a printing platen, at least one printing material string output by the at least one printing head; providing a rod-shaped heating device movably arranged over the printing platen; controlling the rod-shaped heating device, via a heat controller, to emit a heat irradiation directed to the printing platen to heat the at least one printing material string to a reaction temperature to trigger a chemical reaction of the at least one printing material of the at least one printing material string; providing at least one motor coupled to the rod-shaped heating device to move it over the printing platen; and controlling the at least one motor, via a motor controller, to move the rod-shaped heating device over the printing platen to harden the at least one printing material string printed on the printing platen.