What Is Polypropylene (PP)? Properties and Uses
One of the most widely used members of the polyolefin family: how is PP produced, what are its standout properties, and which industries use it?
Definition and production
Polypropylene (PP) is a thermoplastic obtained by polymerizing the monomer propylene (propene). Production typically uses Ziegler-Natta or metallocene catalysts; the catalyst type and polymerization conditions determine the molecular structure of the resulting PP and, in turn, its final properties.
Together with polyethylene, PP is one of the two major members of the polyolefin family and one of the most widely produced plastics in the world — its light weight, low cost and broad range of applications are the main reasons for this.
Standout properties
Low density: a relatively light material among polyolefins (approximately 0.90-0.91 g/cm³), which means more products/parts can be made from the same weight.
High melting temperature: melts at around 160-170°C, making it more heat-resistant than many polyethylene types — a preferred choice for applications such as sterilizable containers and hot-fill packaging.
Chemical resistance: shows good resistance to acids, bases and many solvents.
Fatigue resistance: withstands repeated flexing — this property is used in particular in 'living hinge' designs (e.g. shampoo cap hinges).
Limited low-temperature performance: homopolymer PP in particular can become brittle below freezing; this is improved in copolymer PP grades (see related article).
Uses
Packaging: food containers, caps/closures, flexible packaging films.
Textiles: widely used in yarn/fiber (BCF carpet yarn, woven sacks, raffia sacks, non-woven fabric) production.
Injection-molded parts: white-goods components, automotive interior parts, furniture fittings, crate/container manufacturing.
Pipe and profile: special PP grades such as PP-R are available, used particularly in hot-water plumbing.
Related articles
The Difference Between Homopolymer PP and Copolymer PP
You'll see 'homopolymer' or 'copolymer' on a spec sheet — this distinction directly affects impact strength, transparency and low-temperature performance.
What Is MFI (Melt Flow Index) and How Do You Read It?
The most frequently asked value on a spec sheet: what does MFI measure, which production method suits low vs. high MFI, and why is the test condition always written next to the value?
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