Polypropylene (PP) is tough, flexible, light, chemically resistant and food safe, which might explain it’s broad range of applications, including engineering plastics, food packaging, textiles and bank notes.
Unfortunately, as a 3D printer material type, PP is notoriously difficult to print with, presenting heavy warping and poor layer adhesion. If not for these issues, PP would likely contend with PLA for most popular 3D printer filament, given its strong mechanical and chemical properties.
Interestingly, since many household objects are made of PP, it’s actually possible to recycle old junk and turn it into new 3D printer material.
WHEN SHOULD I USE PP?
If you can wrest PP’s warping under control, then most prints calling for a hardy and light material would suit PP. It’s important to note however that while the material sees great use in the packaging of consumables and medicine for its food-safe properties, the process of FDM 3D printing negates this with hundreds (if not thousands) of layer lines for bacteria to hang out in — best not to try.