Zylon (IUPAC name: poly(p-phenylene-2,6-benzobisoxazole)) is a trademarked name for a range of thermoset liquid-crystalline polyoxazole. This synthetic polymer material was invented and developed by SRI International in the 1980s and is manufactured by the Toyobo Corporation. In generic usage, the fiber is referred to as PBO.
Zylon has 5.8 GPa of tensile strength, which is 1.6 times that of Kevlar. Like Kevlar, Zylon is used in a number of applications that require very high strength with excellent thermal stability. Tennis racquets, table-tennis blades, snowboards, various medical applications, and some of the Martian rovers are some of the better-known instances.
Zylon gained wide use in U.S. police officers body armor protection in 1998 with its introduction by Second Chance Body Armor, Inc. But protective vests constructed with Zylon became controversial in late 2003 when Oceanside, CA Police Officer Tony Zeppetella's and Forest Hills, PA Police Officer Ed Limbacher's vests failed, leaving Zeppetella mortally wounded and Limbacher seriously injured. Some studies subsequently reported that the Zylon vests may degrade rapidly, leaving wearers with significantly less protection than expected. Second Chance eventually recalled all of its zylon-containing vests, which led to its subsequent bankruptcy. In early 2005, Armor Holdings, Inc. first recalled its existing Zylon-based products, and decreased the rated lifespan warranty of new vests from 60 months to 30 months. In August 2005, AHI decided to discontinue manufacturing all of its Zylon-containing vests. This was largely based on the actions of the U.S. government's National Institute of Justice, which decertified Zylon for use in its approved models of ballistic vests for law enforcement. 
Space elevator research
A competition was held in the Wirefly X Prize Cup in Las Cruces, New Mexico, US, on October 20–21, 2006. A team from the University of British Columbia entered into the Tether Challenge, using a construction made from Zylon fibers. The house tether used by Spaceward, that the other teams would have to beat in strength by 50% in the 2007 Spaceward games, was made of Zylon.
High-altitude balloon science
Zylon is used by NASA in long-duration, high-altitude data collection. Braided Zylon strands maintain the structure of polyethylene superpressure balloons. Zylon is the material of choice due to its low weight, high tensile strength, and thermal properties.
As has been the case since 2001, Zylon tethers are used in Formula One to affix the wheel to the chassis thus preventing the wheel from ejecting in to a crowded area in the event of an accident which causes the wheel to become airborne. Starting in the 2007 season, the driver's cockpit must now be clad in special anti-penetration panels made of Zylon. In 2011, a Zylon strip was introduced to reinforce the top of the racing helmet visor and provide an overlap between the visor and helmet for additional protection after Felipe Massa's 2009 injury. The Indy Racing League began using Zylon in 2008.
On modern racing yachts Zylon is used for parts of the standing rigging. It is used as shrouds and stays. The PBO (polybenzoxazole) fiber is degraded by UV and visible light, seawater and chafing, and is therefore protected by a synthetic melted-on jacket. It is claimed to be 65% lighter than traditional rigging at 110–130% of the price of rodrigging. Based on laboratory tests, superior durability is also claimed. Zylon has a high Young's modulus of 270 GPa, meaning that it is very stiff.
Zylon has been incorporated as the base fiber for some conductive textiles, where the Zylon fiber is plated with nickel, copper, silver, or gold. The conductive fiber is used for electronic textiles, EMI shielding in woven or knit sheets, or as a braid over wires, and for signal transmission or current conduction. This conductive fiber combines the advantages of Zylon (strength, resistance to high temperatures, durability, light weight, etc.) with the electrical properties of various metals. The conductive yarns can be sewn, braided, knit, or simply insulated like a bare wire.
PBO is the strongest and stiffest of commercially available fibers used to repair and strengthen concrete and masonry structures in externally bonded composite systems. In this system, the fibers are produced in the form of a fabric mesh, and a cementitious mortar matrix bonds this to an existing structure.
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