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Polyurethane foam packing material. Image Credit: Shutterstock.com/Louella938

Polypropylene vs. Polyurethane: Material Differences and Comparisons

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

Xomety X
By Team Xometry
January 6, 2023
 5 min read
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Polypropylene and polyurethane serve many of the same purposes. However, each presents its own trade-offs. Polypropylene is created through the polymerization of propylene monomers while polyurethane is produced by reacting a diisocyanate with a polyol. Polyurethane is subdivided into two types: thermosetting and thermoplastic polyurethane. 

Polypropylene (which is appropriate for injection molding and thermoforming) and polyurethane (good for reaction injection molding, casting, and extrusion blow molding) have many similar applications. They are used in the production of bottles, toys, wire insulation, etc. This article will further discuss and compare the physical properties, applications, and cost of polypropylene vs. polyurethane.

What is Polypropylene?

Polypropylene is a thermoplastic that is manufactured through the polymerization or combination of propylene monomers. It is a worthy replacement material for common conventional plastic products and finds relevance in many industrial processes. Polypropylene comes in handy in the production of belt covers, living hinges, textiles, container lids, and buffers, to name a few. For more information, see our guide on What are Polypropylene Plastics.

Figure 1 is an example of Polypropylene:

Slide 1 of 1
close up of polypropylene
close up of polypropylene
close up of polypropylene

An example of polypropylene granules.

Image Credit: Shutterstock.com/Afanasiev Andrii

Additionally, polypropylene resists certain solvents, both acid, and base. For this reason, its products can be used as containers for slightly acidic solutions. Among its physical properties are high strength, good fatigue resistance, and resilience in moist environments. Relevant manufacturing processes include injection molding and thermoforming. 

What is Polyurethane?

Polyurethane comes in both thermoset and thermoplastic forms. Both are created in chemical reactions that take place between diisocyanate and polyol. The thermoset variety should not be confused with a thermoplastic. Though both of them are polymers, they do not behave the same way when exposed to heat. Unlike thermoplastics, thermosetting materials cannot be melted or remolded. Any attempt to reheat a thermoset item will only char it. However, this is not always a disadvantage because, in high-temperature applications, thermoset polyurethane is more capable than polypropylene. Figure 2 is an example of polyurethane:

Slide 1 of 1
gray and yellow polyurethane foam
gray and yellow polyurethane foam
gray and yellow polyurethane foam

An examples of polyurethane foam.

Image Credit: Shutterstock.com/Andrew Safonov

Polyurethane offers flexibility in design. It can be tailored to make the surface as soft as foam or as rigid as metal. Polyurethane can be used to manufacture a lot of parts including: cushioning for furniture, shoe soles, car parts, insulation for refrigerators, rollers, and sportswear. Water, grease, and oil do not affect the stability of polyurethane. Moreover, it bonds well with other materials such as wood, metals, and other plastics. The adaptability and design flexibility of polyurethanes make them convenient for manufacturing processes such as reaction injection molding (RIM), casting, thermoforming, and extrusion blow molding.

Polypropylene vs. Polyurethane: Applications and Uses

When it comes to applications, polypropylene and polyurethane offer many similar benefits. They are used for packaging food and drinks. Both can also be used to make toys, clothing, and other household items. Polyurethane is very common as insulation or soundproofing in buildings. It can also be employed as a coating on other materials to protect them from moisture or UV rays. 

Polypropylene vs. Polyurethane: Physical Properties

Table 1 below highlights the chemical properties of polypropylene vs. polyurethane:

Table 1: Comparison of Polypropylene vs. Polyurethane Properties
Physical PropertiesPolypropylenePolyurethane
Physical Properties

Chemical resistance

Polypropylene

High chemical resistance

Polyurethane

High chemical resistance

Physical Properties

Tensile strength

Polypropylene

4,800 psi 

Polyurethane

200-800 psi

Physical Properties

Density

Polypropylene

0.90-0.92 g/cm3

Polyurethane

0.05 - 1.7 g/cm3

Physical Properties

Impact tolerance

Polypropylene

Good impact tolerance or resistance

Polyurethane

Good impact tolerance or resistance

Physical Properties

Water absorption

Polypropylene

Resistant to absorbing water or moisture

Polyurethane

Resistant to absorbing water or moisture

Physical Properties

Surface hardness

Polypropylene

74-76 on the shore D hardness scale 

Polyurethane

It has a wide range of 55 shore A to 75 shore D  hardness scale 

Physical Properties

Operating temperature

Polypropylene

180°F (82.2°C)

Polyurethane

-80°F to 200°F (-62°C to 93°C)

Polyurethane performance can be extended to temperatures upwards of 300°C (150°C) with certain formulations

Physical Properties

Melting temperature

Polypropylene

160 °C

Polyurethane

Thermoplastic polyurethane has a melting point of 163°C. Thermosetting polyurethane either combust or loses its valuable properties when overheated.

Polypropylene vs. Polyurethane: Recyclability and Sustainability

Polypropylene is recyclable but is not so sustainable. It is an environmentally friendly option that offers a lot of benefits compared to other materials. Polypropylene, unlike polycarbonate, does not significantly affect the health of humans. As a result of its tolerance to heat and the fact that it does not leach chemicals into food, it is used as packaging in many food and beverage industries. However, it has a drawback. When it is heated to very high temperatures it can cause a medical condition called occupational asthma. 

Polypropylene, according to a trade publication for the clean technology industry called AZoCleantech, can pass through a recycling process four times. On the other hand, polyurethanes are less environmentally problematic because they use less energy to produce. Some versions are also biodegradable. Thermoplastic polyurethane is recyclable while thermosetting polyurethane is not. 

Polypropylene vs. Polyurethane: Cost

The cost of polypropylene is somewhere between $0.55-0.89 per kilogram while thermosetting polyurethane and thermoplastic polyurethane cost about $6.10 and $5.50 per kilogram, respectively.

Alternative Materials to Polypropylene and Polyurethane

Polyethylene, an alternative material to polypropylene and polyurethane, is a synthetic resin that is made by polymerizing ethylene molecules. It is among the most popular consumer plastics. Polyurethane is a thermoplastic material, meaning that when heat is applied, it liquefies and exhibits identical properties after cooling and resolidifying. Polyethylene products can be recycled many times before the material becomes useless. Some uses of polyethylene include but are not limited to grocery bags, bottles, food and drink packaging, and wire and cable insulation.

Summary

This article presented polypropylene and polyurethane, explained what they are, and discussed the applications and properties of each material. To learn more about polypropylene and polyurethane, 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.