The invention relates to a print head (10) for a 3D printer (1), comprising a feed zone (11) with a feed (12) for feedstock (20) with variable viscosity, a melting zone (14) comprising a heating element (15) and an outlet opening (16) for the liquid phase (22) of said feedstock (20), as well as a conveyor device (30) for conveying the feedstock (20) from the feed zone (11) into the melting zone (14), said conveyor device (30) comprising a plunger (31) that can be inserted into said feed zone (11).