While polypropylene and polyurethanes may look and feel the same, both materials offer different physical properties and manufacturing processes. In this post, we will discuss these differences and when to choose the best material for your product design.
What is Polypropylene?
Polypropylene (PP) is created through the polymerization of propylene gas. Thermoplastics like polypropylene and polyethylene liquefy under high heat, which allow these materials to easily take shape generally through injection molding or thermoforming. Because of this, polypropylene can display a wide range of properties based on the chosen manufacturing method. While polypropylene may have many similarities to polyethylene, polyurethanes tend to offer more robust physical properties even in the most extreme environments.
What is Polyurethane?
Unlike polypropylene, polyurethane is a thermoset formed through the chemical reaction between a polyol and diisocyanate. Despite having a complex chemical structure, this unique material can allow engineers to tailor the urethane's chemistry to meet specific design requirements. For instance, polyurethanes can be custom formulated to be either soft and flexible as a cushion to something hard and rigid like metal. Due to their adaptability, this unique material can offer unlimited design freedom through a cast or Reaction Injection Molded (RIM) process.
Differences Between Polypropylene & Polyurethane
Despite having similar names, polyethylene and polyurethanes differ significantly. As an example, the table below breaks down these variations to help discern between the two sought-after materials:
| Polypropylene | Polyurethane |
| Commonly injection molded or thermoformed | Commonly cast or Reaction Injection Molded (RIM) |
| Limited durometers available | Can be custom formulated to meet exact design needs |
| Low resistance to heat | Able to withstand temperatures between -80°F up to 300°F |
| Difficult to bond | Can bond to various subcomponents |
| Can be made conductive through the use of carbon black | Can be made conductive without the use of carbon black |
Which Material Should You Choose?
Depending on your design requirements, polypropylene and polyurethane can fit into a wide range of products and components. However, polyurethanes can produce stronger, more robust products that can withstand most environmental conditions. For this reason, this versatile material is often considered for applications, such as military & defense, industrial, medical, and packaging to name a few. Polypropylene, typically is best for products that have little to no importance in longevity or wear-life. For example, this material can generally be found in consumer products and packaging industries. When evaluating between both materials, it is important to consider the key physical properties required for better performance.
If you are seeking material assistance for your RIM product design, complete our design tool, here, or download our Durethane data sheet, below, to explore the superior properties available.
