On the surface, ExOne (NASDAQ:XONE) and voxeljet (NYSE:VJET) are very similar 3-D printing companies. Both compete in the industrial segment, use a similar 3-D printing technology, and boast some of the largest print beds in the world.

Where these two companies differ boils down to the materials they can print with. Voxeljet only offers 3-D printing in two different types of plastic and one type of sand. ExOne, on the other hand, offers 3-D printing in two different types of sand, five types of metals with seven different finishes, and a soda lime glass that's available in three different finishes.

This greater range of materials gives ExOne a competitive advantage over voxeljet, Motley Fool contributor Steve Heller argues. With more materials, ExOne can serve a greater base of customers and has a larger business opportunity than voxeljet. Check out the video below to get the full story.