[ThenAsNow]

Conventional ways to do this include casting or, as is done on the RL-10 and SSME, building the nozzle out of thin-walled tubes (very labor-intensive and expensive). 3D printing is the future here, but there's still lots of improvement required in terms of wall thickness and roughness control, not to mention build volume.

[avmich]

The previous phrase was that the part is lost-wax cast. To me it's interesting how one can build cooling channels in the part which is cast.