The last three chapters talked you through the process of creating a 3D model, running slicing software to create printer commands, and finally loading it onto a printer and running it. This chapter goes into a few situations that are a little different than the straightforward one of creating a solid object. What happens if you want an object that is hollow inside (no infill), or that is shaped like a vase (solid bottom, but no infill or top)? And how do the directions we have given so far extend to 3D printers that have more than one extruder, to print in multiple materials? We go through an example of each in this chapter.