Ordinarily, when using an off-the-shelf 3D printer, it’s quite difficult to print a single object that incorporates multiple materials. An experimental new system could make it easier, though, by utilizing a “programmable filament.”
Most consumer-grade 3D printers create objects via a process known as fused deposition modelling. This involves loading them up with a spool of polymer filament, which they subsequently heat to the melting point, then extrude out of their print nozzle. In this way, they build items up, one horizontal layer at a time.
If you want to 3D-print an object that incorporates multiple types of polymer (such as ones of different colors), you usually have to swap the various polymer filament spools in and out of the printer, as it’s printing the different parts of the object.
This can conceivably get very fiddly. If you were printing a vase with differently colored vertical stripes down the sides, for instance, you would have to swap between filaments on every printed layer. That’s where the programmable filament system comes in.