The ZPrinter 450 uses powder as a support material. This solves a lot of problems and allows the support material to be reused. Obviously it does require some kind of enclosure to prevent air movement.

Its also useless for this type of replication that the RepRap use.

We would have to come up with a formula that can be easily dissolved and some physical strength

Oh...it's really prints like a 2D printers!

See the color cartridge? It's just standard HP inkjet color cartridge! (I think they license their technology?)

And I think somehow the inks react with the powder so they forms solid.
But then it's not plastic right? I suspect the strength of those powder formed thing will be much less than ABS.

[www.uprintsource.com] UPrint is also interesting, I think it prints like RepRap. I am not sure how they figure out the support though.

The ZPrinter 450 builds objects from corn starch, which gets sticky on contact with water-based ink-jet printer ink. The objects produced are very weak an only usable as mock-ups; the glow-plug engine shown in the film would break into pieces if you actually tried to use it.