PBO (Poly (p-phenylene-2, 6-benzobisoxazole)) is liquid crystal polymer developed by Japan-based Toyobo under the trade name Zylon.
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PEN (Polyethylene naphthalate), commonly known by Honeywell's trade name "Pentex", is another kind of polyester fiber, which stretches only 40% as much as standard PET fibers, but about twice as much as Kevlar 29.