I have used 3D printing. I can’t imagine anything produced from that would be able to stand the rigors of launch and the vacuum of space. What material are they using? Some super epoxy I imagine. Wow if true.
I'm not sure. They are either printing it out of high-temperature metal, or they are printing lost-wax molds and then using them to cast the engines.
It's pretty exciting, though. The most efficient engines are those that use expansion nozzles that are entirely fabricated out of thin-walled tubing. This is what was used on all the manned space flights, including the Space Shuttle. Unfortunately, these are quite expensive.
If they can be made by 3-D printing, it's a huge breakthrough. This is one of the angles the big guys are looking at.
3-D printing using liquid metals is a hot field. In more ways than one.
3D printing metal.
http://3dprinting.com/metal/