…NASA didn’t use ABS plastic that most 3D-printers use. Instead, the agency used custom 3D printers to spray layers of metallic powder using lasers. The lasers spray the powder in a specific pattern in order to come up with the desired shape for an object. In this case: a rocket engine injector.
Read more at: Slash/Gear http://www.slashgear.com/nasa-3d-printed-rocket-injector-undergoes-first-test-firing-12290238/