Polypropylene (PP) is a thermoplastic that has a number of properties that sets it apart from other thermoplastics which see common use with 3D printing, including PLA, ABS and nylon (PA).

This is of course not limited to this brand of printers, and affects all extruder ... slurry made from saturating a bottle of acetone with ABS leftovers. In the clip after the break he shows ...