We may not have landed humans on Mars yet, but NASA is already considering how to help them stay long term.

For the last five years, engineers at NASA's Swamp Works laboratory in Kennedy Space Center have been working on how to construct buildings on the surface of the moon and Mars, Fast Company reports. The method they are using employs 3D printers, which have already succeeded in producing road barriers — a more difficult task than it might seem.

3D printing is a way to avoid humans having to undertake physical labor in the harsh environment of space, but finding or transporting material out of which to build is just as much an issue, and Swamp Works has thought of a creative solution.

The printers will use a combination of regolith, or crushed rocks that are found on the surface of both Mars and the moon, and a polymer made of recycled plastic. The recycling technology was assisted by Autodesk, which now plans to integrate some of the tech here on Earth by recycling plastic and regolith into industrial construction, according to Fast Company.

The U.S. Army has also partnered with NASA for field construction using trash and local rocks, further expanding the program's possible uses on Earth. In space, plastic could possibly be synthesized from carbon on Mars or even greenhouse-grown corn.

As for what the buildings might actually look like, NASA is holding a competition among engineers, which has progressed to five finalists that will be building their own 3D printers for scale prototypes, due in 2019. The winning team will win $2M, and if the project gets funding, Swamp Works estimates it can get a prototype built on Mars in five years.