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How to select plastic resin for molding (easy method)

Updated: Jul 6, 2021

There are more than 75,000 different types of plastic that are used in injection molding.


They have tradenames like Delrin, Santoprene, Plexiglas, and Kydex.

How can a designer keep them all straight?

Our goal is to select the perfect resin but the vast list of materials in the market can be overwhelming.

Let me simplify it for you:

I'll teach you a couple of ways that work for me.

Basic Method:

Here's the basic (shoot from the hip) method for plastic resin specification:

Stick to Default: Select PC, ABS, or PC+ABS for molded parts.

A high percentage of plastic parts in the world are ABS, PC, or a blend of the two.

ABS is a medium-cost thermoplastic that's easy to process, and PC is added to increase stiffness and scratch resistance. HIgher blends of PC can hold a higher polished surface. Higher blends of ABS will be more flexible.

Is cost a concern? Downgrade to PS, PE, or PP

Polystyrene (PS) Polyethelyne (PE) and Polypropylene (PP) are some of the lowest-cost resins, and are typically used in disposable or low-cost parts.

Need Flexibilty? Select PP, TPE, or Nylon

Living hinges (flexibility in hinged sections) of molded parts basically limits you to PP. Nothing compares to PP for flexibility. Think pill organizers with their integrated molded lids.

Thermo-Plastic Elastomers (TPE) come in a variety of durometers (soft to hard) that fit your application. Choose soft durometer for hand grips and high durometer for shoe soles.

Need Optical Clarity? Select PS/HIPS, MABS, or Acrylic

Polycarbonate (PC) is typically used for safety glasses for impact and scratch resistance.

Polystyrene (PS) and it's counterpart Hi-Impact Polystyrene (HIPS) are lower-cost variants, with much more brittle. PS is common for toys and cheap throw-away parts.

Sliding or Motion? Choose Nylon, Acetal/POM, or Delrin. Gears, mechanisms or other mechanical applications typically use these resins. These plastic blends have self-lubricating properties that help prevent galling of contacting surfaces.

Additives: Plastic resins can also have fillers/additives for changing properties.

Some examples of fillers are:

  1. Glass fibers for stiffness

  2. Glass beads for surface finish

  3. Carbon fibers for lightweight or conductivity

  4. Others..

This is a very simplified selection guide.

Next week I'll cover a more complex, scientific method that covers Amorphous/Semi-crystalline plastic selection and chemical resistance. I'll also share a plastic selection guideline that will help walk you through this process.

I'd love to help you accelerate your design and prototyping projects!

Call me if you have any questions on your next plastics project: 763-229-9516


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