Back In 2013, Dennon Oosterman and his former classmates Alex Kay and David Joyce grew tired of churning through expensive filament for their 3D printer. So they built a machine that could recycle it back into usable form. The $700 ProtoCycler now released grinds scrap plastic — such as empty bottles and rejected 3D-printed models — into digestible pieces, melts it down, extrudes it, and winds it onto a spool. To ensure consistency, a computer-controlled diameter-feedback system uses two cameras to accurately measure the width of the filament.

There are a few drawbacks to recycled plastic. Although the Proto­Cycler’s filament starts out with about the same strength as the standard stuff, it gets weaker with each reuse. Reprinting your model too many times might make it brittle and frail. Multicolored plastic also blends like paint. This isn’t a problem at first, but eventually your filament will end up brown. None of that is a big deal if you’re using the printer to rapidly prototype designs, when quantity matters more than quality.