Abstract: A fused filament fabrication system (1) is described comprising a number of print heads (31,32,33), a print head mount (4) arranged for releasable connection with any of the print heads and a gantry (5) arranged to move the print head mount (4). So-called filament modules (61,62,62) are provided that can be connected to the print heads (31,32,33). The print heads can be docked into a special print head dock (8) or they can be docked into one of the filament docks (71,72,72) if a filament module is arranged in between. A number of filament feeders (9) is arranged for feeding filament (11) to the respective filament modules. A control system (25) is arranged to control the gantry so as to select one print head from the number of print heads, to obtain a selected print head (31). The selected print head can be used for a printing job having the current filament attached, or it can be moved to another filament dock to first pickup a different filament.