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It’s a simplistic question, possibly even naive. Put it to a chemical engineer or a materials scientist, and she or he will almost certainly not come back with a single answer, but with (at least) two questions:

  1. What do you mean by “plastic?” Do thermosetting materials like epoxy count? What about polymers that are reinforced with glass or carbon fiber infill?
  2. What do you mean by “strong?” Are you talking about wear resistance? Compressive or tensile strength? Temperature resistance? Chemical resistance?

But say you limit your question to thermoplastic materials that can be melted and molded, extruded, spun, and/or drawn into various shapes. And that you exclude composite materials of any kind—just pure polymers without any reinforcement or infill.

Given those answers to question 1, a single material begins to stand out almost regardless of how you answer question 2.

That material is polybenzimidazole (PBI), marketed as a bulk polymer under the trade name Celazole. It is commonly reported to have the highest compressive strength of any unfilled plastic material, and also has the highest tensile strength, highest shear strength, and highest Rockwell hardness rating of any plastic that I have been able to find. It maintains its mechanical properties at high temperatures better than any other unreinforced polymer, and can reportedly survive short-term exposure to 1400°F, which is 200° above the melting point of aluminum. Phrases like “the highest performing engineering thermoplastic available today” are commonly used to describe Celazole in plastics industry literature.

NASA identifies PBI as a space program spinoff technology, and maintains an informative page describing its history, which, in fiber form, includes astronaut flight suits used on Apollo, Skylab, and numerous space shuttle missions.

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. I wonder how much it costs.

  2. greyfade says:

    … And it is *not* cheap. 3/8″ rods can cost as much as $225 *per foot*.

    I’m curious what other high-performance plastics there are that might be more affordable. :)

    1. Jason says:

      I would say “eep!” but truly I am not surprised.

      Dang cool though.

    2. Simon says:

      Well if it costs that much, you might as well just use metal.

      1. Depends on your application. Calezole is used in specialty applications because it has high ultrasonic transparency, which is not a common property in metal. Also, obviously, it’s nonferrous which matters in some applications. It’s non-conductive, has low coefficients of friction and thermal expansion, is a pretty darned good thermal insulator and is far more chemically resistant than most metals. It’s often used in the manufacture of semiconductors and flat panel displays. Before you rush right out and buy it for your next project though, you should know that machining it is a first class pain in the butt; diamond coated or polycrystalline tooling is recommended.

  3. Jason says:

    Stop teasing me! Where can I get some! :)

    1. You can buy it from Professional Plastics, if you wish. A 12″x12″x.5″ sheet is only $2169.01, and 1″ diameter rod is a trifling $1180.18 per foot.

  4. rocketguy1701 says:

    As cool as it is, I suddenly realized that unless you have a truly compelling reason to use it, it’s exactly the sort of stuff that shouldn’t enter the waste stream.

    I’m gonna stick to PLA for now, and ABS when I’m going to keep it for a long time. At least I can recycle that. And metal for those applications where strength or temperature resistance is more of an issue.

  5. Considering PBI a thermoplastic material in the maker sense of the word is a bit of a stretch… If you’re melting/molding it you might as well use Al.

  6. Astrolite says:

    While polybenzimidazole has excellent tensile strength, it has sacrificed almost all its ductility to get there. I think it has an elongation before break of about 3%. In other words, it behaves more like a brittle ceramic than common thermoplastics. I would say PEEK is the highest performing not crazily impractical plastic.

    1. Sean Ragan says:

      Great comment, thank you!

  7. Bob says:

    I would suggest Ultra High Molecular Weight Polyethylene (UHMWPE). Its the stuff they eventually turn into fibers for bullet-proof(resistant) vests and the fiber in carbon fiber. It has decent wear resistance, and is used in a lot of industrial machinery.

    Yes, it is essentially the same polymer they make plastic bags out of, but funny things happen when you increase the molecular weight enough.

    Plus, its plastic bag cheap!

  8. Chuck Hillery says:

    Okay, let’s make it more practical. Suppose, for whatever reason, you wanted to make a 250 foot flagpole of something that would not conduct electricity. Keep in mind that it would need to support a huge flag, let’s imagine 20′x40′, during high winds and not bend. Let’s further suppose that you would want something with some weight at the top, such as a satellite antennae. You would also want this to last as long as possible, since it would probably be a bit of a pain to replace. Which plastic would you use, then?

  9. bea says:

    can i make it?