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Polypropylene rolls for packaging. Image Credit: Shutterstock.com/AYRAT ALPAROV

Polypropylene vs. Polyethylene: Material Differences and Comparisons

Learn more about the applications and properties of these two materials.

Xomety X
By Team Xometry
December 23, 2022
 6 min read
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When comparing polypropylene vs. polyethylene you’ll find they have a lot in common. They find use across many industries, and both polymers have very similar chemical structures. However, there are also some key differences between the two that need to be considered. 

Polypropylene (PP) and polyethylene (PE) both belong to the thermoplastic family. Depending on the grade, they can be melted and reformed multiple times. Polypropylene is a polyolefin, which means that it is made up of repeating units of propylene. Polyethylene, on the other hand, while also a polyolefin, can be made from a variety of different monomers, the most common being ethylene. 

Of the two, polypropylene can withstand higher temperatures. It is more rigid and has a higher melting point than polyethylene. Also, polypropylene is used in food packaging, as it is food-safe and moisture-resistant. Polypropylene finds its way into packaging, carpets, ropes, and plastic parts. 

Polyethylene is widely used in packaging as well since it is very strong and durable. This includes food packaging. Other common places to find polyethylene are cable and wire insulation, toys, buckets, and grocery bags. In this article, we will compare polypropylene vs. polyethylene in terms of its properties, applications, and more.

What is Polypropylene?

Polypropylene (PP) is a thermoplastic polymer that belongs to the polyolefin family. It is made up of repeating units of propylene and can be made through various different manufacturing processes, including injection molding and extrusion. For more information, see our guide on All About Polypropylene.

Figure 1 below are examples of Polypropylene (PP) pellets:

Slide 1 of 1
dark and medium blue polypropylene pellets
dark and medium blue polypropylene pellets
dark and medium blue polypropylene pellets

Close up of polypropylene pellets.

Image Credit: Shutterstock.com/sveticluka

Polypropylene is a versatile polymer that can be found in: packaging for food and other consumer goods, carpets, and ropes. Some common characteristics of polypropylene include

  1. High melting point
  2. Good chemical resistance
  3. Good moisture resistance
  4. Rigidity

Since polypropylene has a high melting point, it can be used in applications where it needs to withstand higher temperatures. Polypropylene is also moisture-resistant, which makes it a good choice for food packaging. Plus, its inherent rigidity gives it good strength and durability.

What is Polyethylene?

Polyethylene (PE) is also a thermoplastic polymer that belongs to the polyolefin family. It can be made from a variety of different monomers, the most common of which is ethylene. Polyethylene products can be manufactured through many different processes, including extrusion and injection molding. For more information, see our guide on What is Polyethylene.

Figure 2 below are examples of polyethylene pellets:

Slide 1 of 1
transparent polyethylene pellets
transparent polyethylene pellets
transparent polyethylene pellets

Transparent polyethylene pellets.

Image Credit: Shutterstock.com/StanislauV

This versatile polymer can be used in various applications, including houseware, bottles, wire insulation, toys, etc. As polyethylene is available in multiple different grades, it can be tailored to meet specific needs. Some common characteristics of polyethylene include:

  1. Good chemical resistance
  2. Good moisture resistance
  3. High impact strength
  4. Flexibility

The most common polyethylene grades are low-density polyethylene (LDPE) and high-density polyethylene (HDPE). LDPE is a soft, flexible polymer that is often used in food packaging and grocery bags. HDPE is a stronger, more rigid polymer that is often used in bottles, pipes, and buckets.

Polypropylene vs. Polyethylene: Applications and Uses

Both polypropylene and polyethylene are versatile polymers that can be used for many different purposes. Some common uses for polypropylene and polyethylene include:

  1. Food packaging
  2. Packaging for other consumer goods
  3. Carpets
  4. Ropes
  5. Buckets
  6. Grocery bags

The two polymers differ, however, and some products can make use of one but not the other. For example, polypropylene is often used in the production of non-translucent materials (though it can be made translucent through a chemical treatment called bleaching). Some polyethylene materials, meanwhile, are naturally translucent.

Polypropylene vs. Polyethylene: Physical Properties

Table 1 below highlights some physical properties of polypropylene vs. polyethylene:

Table 1: Properties of Polypropylene and Polyethylene
Physical PropertiesPolypropylenePolyethylene
Physical Properties

Chemical Resistance

Polypropylene

High chemical resistance

Polyethylene

Very high chemical resistance

Physical Properties

Tensile Strength

Polypropylene

0.5-3.0 GPa

Polyethylene

3.7-19 Gpa

Physical Properties

Impact Tolerance

Polypropylene

Good impact tolerance or resistance

Polyethylene

Good impact tolerance or resistance

Physical Properties

Water Absorption

Polypropylene

Resists water absorption

Polyethylene

Resists water absorption

Physical Properties

Surface Hardness

Polypropylene

92 on the Rockwell R scale 

Polyethylene

-

Physical Properties

Translucency

Polypropylene

Naturally opaque in color but can be made translucent

Polyethylene

Some variants are translucent

Physical Properties

Static Charge

Polypropylene

Higher static charge

Polyethylene

Lower static charge

Physical Properties

Purity

Polypropylene

Is often co-polymerized with ethylene 

Polyethylene

The purity level is often 100% 

Physical Properties

Operating Temperature

Polypropylene

82.2 °C (180 °F)

Polyethylene

-

Physical Properties

Melting Temperature

Polypropylene

163.8 °C (327 °F)

Polyethylene

Low-density polyethylene melts at 110 °C (230 °F) while High-density polyethylene melts at 120 °C (250 °F)

Polypropylene vs. Polyethylene: Recyclability and Sustainability

Polypropylene and polyethylene are both recyclable materials. Polypropylene can be recycled up to four times. High-density polyethylene can be recycled up to ten times while low-density polyethylene can only take one recycle.  This makes high-density polyethylene a far more sustainable material. 

Polypropylene vs. Polyethylene: Cost

Polypropylene costs about $0.55-0.80 per kilogram while polyethylene costs about $0.80-1.60 per kilogram. The actual cost depends on the specific grade that is being used, but polypropylene is generally less expensive than polyethylene. 

Alternative Materials to Polypropylene and Polyethylene

Listed below are some alternative materials to both polypropylene and polyethylene:

  1. Polystyrene: Polystyrene is a rigid thermoplastic polymer in the polyolefin family. It can be made from a variety of monomers, the most common being styrene. Injection molding is used to manufacture many polystyrene products. Polystyrene is commonly used in packaging, insulation, and construction.
  2. Polyvinyl Chloride (PVC): PVC is a thermoplastic polymer that belongs to the polyolefin family. Vinyl chloride is the most common monomer used in its production. PVC can be produced in both rigid and flexible variations and is often seen in the form of pipes, cables, and window frames. Dioxins are created as by-products of the PVC production process, which can have negative effects on the environment
  3. Polycarbonate: Polycarbonate is a thermoplastic polymer that belongs to the polyolefin family. It can contain a variety of monomers, the most common of which is bisphenol A. Polycarbonate is often used as a substitute for polypropylene in applications that require both impact resistance and transparency.

Summary

This article presented polypropylene and polyethylene, explained what they are, and discussed when to use each one in manufacturing. To learn more about polypropylene and polyethylene, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.