Polypropylene (PP) is a tough, flexible plastic that is rarely used in 3D printing
It has many desirable characteristics, including the fact that it doesn’t absorb water, and is chemically resistant and resilient to bending
The main issues with 3D printing with PP are that it shrinks significantly and is difficult to get to stick to the bed during printing; using polypropylene tape as a surface helps.
Despite these challenges, PP could be a useful material for 3D printing water-resistant parts or compliant mechanisms, for example.
Last year Hackaday featured a guide to getting started with PP 3D printing, and it is also possible to make your own PP filament from old face masks.
