There are many plastics to choose from when you’re planning a manufacturing or fabrication project. To find the best material, start by thinking about the application and environment. What does the plastic part or product need to do? And where will it be doing it? These questions can help you better understand what plastic characteristics you need:

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  • What range of temperatures does it need to withstand?
  • Will it be exposed to chemicals or other harsh conditions?
  • Will it be used outdoors and exposed to UV light?
  • Is it a structural piece requiring strength and dimensional stability?
  • Is it for a bearing-and-wear application requiring a low-friction surface and high wear resistance?
  • What is its expected lifespan?
  • What kind of load does it need to withstand?

The Polymer Pyramid

The polymer pyramid (also called the plastics pyramid) is a common way of thinking about the range of plastic materials and their general characteristics. These are the three levels of the pyramid, beginning with the base.

 

 

Standard plastics, also called commodity plastics, are relatively inexpensive and are good for noncritical applications that don’t require outstanding thermal or mechanical properties.

Engineering plastics have better thermal or mechanical properties and are generally suitable for bearing-and-wear applications.

Advanced engineering plastics, also called high-performance plastics, have even better thermal or mechanical properties and are suitable for more demanding applications. Imidized plastics such as PAI offer the best performance.

The plastics on the left side of the pyramid are amorphous polymers, while those on the right side are semi-crystalline polymers. This distinction is based on whether the molecules that make up the plastic are arranged in a more random or in a more orderly way. The chart below summarizes the general properties of amorphous and semi-crystalline plastics.

Key Characteristics of Amorphous vs. Semi-Crystalline Plastics