Polypropylene is an opaque, semi-crystalline plastic. It's commonly used plastic utensils and Tupperware. In packaging, it's often used for labels, stickers, and tape.
It's a thermoplastic which means it melts when heated to a certain temperature. This makes it a viable option for injection molding. On its own, it has very low density. To improve its strength, it can be combined with other plastics (or even fiberglass) to improve its strength and durability.
Can have high clarity
High resistance to chemicals
High resistance to moisture
High melting point
High resistance to cracking
Resistant to leaching
Resin code #5, very low likelihood of recyclability
Not resistant to UV light, will degrade over time
Derived from fossil fuels