The Replicating Rapid-prototyper printer (RepRap) is an open source, self-copying 3D printer that works by building objects in layers of plastic, primarily polylactic acid, a bio-degradable polymer made from lactic acid. Unlike existing prototyping printers, RepRap can replicate and update itself, including printing its own parts, says RepRap software developer Vik Olliver. The RepRap development team, is spread throughout New Zealand, the United Kingdom, and the United States. By making the project open source, the team hopes to be able to continue to improve the machine until it can do what people want it to do. Improvements received by the team are then sent back to users, allowing RepRap to evolve as a whole. A recent feature added to RepRap are heads that can be changed for different kinds of plastic. Olliver says a head that deposits low melting-point metal is in development, which means low melting-point metal could be put inside higher melting-point plastic, allowing for the production of structures such as motors. RepRap could also allow people to build circuits in 3D and in various shapes. Having the machine be able to copy itself is the most useful feature the team can give it and is the primary goal of the project, Olliver says.