Just like the ink that goes into 2D printers, the plastic filament used by 3D printers is expensive. And it’s bound to get more expensive as manufacturers begin adopting proprietary filament cartridges that limit users’ options.

Instead of paying $30 to $50 for 2.2 pounds of plastic, an emerging option is to recycle plastic from used packaging and other household items. For a few hundred dollars, you can buy or make a recycling machine small enough to fit on your desk.

A study conducted by Michigan Technological University found that it is really good for the environment too. Researchers tracked how much energy went into recycling a plastic milk jug and found that people reusing them for home 3D printing consumed less energy than sending them to a traditional recycling plant.

Energy savings were relatively minor in cities, where home recycling used just 3 percent less energy. But in smaller cities…