Polypropylene Density | All You Need To Know

Hey guys, polypropylene is one of the most produced plastic materials worldwide. Let’s go through a piece explaining PP density in detail.

Polypropylene Density

A plastic material’s density is described as the mass per unit volume of a material, generally measured in grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³).

The density of polypropylene can range from 0.90 to 0.94 g/cm³, or 900–920 kg/m3, depending on its configuration and manufacturing process.

Grades of polypropylene with a lower density feature a lower molecular weight and fewer long chains, leading to a lower plastic density. One of the key features of polypropylene is, in fact, its low density, which makes it suitable for applications where weight reduction is essential such as automotive, packaging, consumer goods, and piping.

The low density makes PP desirable for injection molding and other manufacturing methods.

Strength and Stiffness

The low weight of PP also affects strength and stiffness. You might think it’s not likely to happen, but polypropylene grades with a higher density possess a higher molecular weight and an increased number of long chains, resulting in improved stiffness and strength.

That property makes polypropylene a fantastic choice for applications requiring high strength and stiffness, such as industrial products, pipes, and electrical components.

The density affects the strength-to-weight ratio of polypropylene, with higher-density grades exhibiting a higher strength-to-weight ratio. However, the stiffness of polypropylene also plays a role in conditioning its strength-to-weight ratio, and a high level of stiffness can make up for a lower density.

Thus, the connection between polypropylene’s density and its other physical properties is intricate and depends on the intended usage.

How Polypropylene’s Density is Affected By The Manufacturing Process?

Yes, the manufacturing process does affect the density of polypropylene. Polypropylene’s density and molecular weight can be altered by manipulating the process conditions during manufacturing, such as the temperature and pressure used during polymerization.

For instance, increasing the polymerization temperature can increase the molecular weight and density of PP, while decreasing the temperature will result in a lower molecular weight and density.

Likewise, changes in pressure during polymerization can impact the density and molecular weight of the final product. Therefore, the processing conditions utilized during the polymerization can be altered to achieve the required density of a particular use case.

Is Polypropylene More Dense Than Water?

Polypropylene has a higher density than water, with an average density of approximately 0.9 g/cm³, while the density of water is 1 g/cm³. As a result, polypropylene will sink in water.


The density of polypropylene is an important property that impacts its processing, performance, and application. The low weight of polypropylene makes it a popular choice for weight-sensitive applications, while the higher-density grades offer improved strength and stiffness.

Polypropylene density can be adjusted by changing the composition and manufacturing process, and its relationship with other physical properties is complex and application-specific.

I hope you liked the article. Keep reading. Have a lovely day.

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