An extruder of a three-dimensional printer may be coupled with one or more filament tubes, each filament tube having its own supply of filament. The extruder may include a drive gear rotatable in a first direction to advance a filament from a filament tube toward at least one extrusion opening defined by the extruder and rotatable in a second direction, opposite the first direction, to advance another filament from a different filament tube toward the at least one extrusion opening defined by the extruder. Also, as one filament is advanced by the drive gear, another filament may be retracted by the drive gear to improve the switching of filaments in a three-dimensional printing process. The extruder may work in conjunction with a filament supply-side drive system that feeds filament into one or more filament tubes, reducing a pull force exerted by the drive gear of the extruder.