Printhead (10) for a 3D printer, comprising an operational volume (17) for holding feedstock (20), the viscosity of which can change, the operational volume (17) being variable by moving a plunger (31, 31a, 31b) and being provided with an outlet (16) through which the feedstock (20) can be extruded by moving the plunger (31, 31a, 31b), the plunger (31, 31a, 31b) being equipped with temperature control means (36).