Future Helmets: Exploring UHMWPE, Carbon Fiber Nanotubes, M5 Fiber & More

UHMWPE fibers have come a long way from humble beginnings. Twenty years ago, it was far from clear they'd enjoy the dominance that they have now come to hold. Back then, the military still utilized Kevlar® in almost all of its body armor systems; Zylon fiber was heralded as the “fiber of the future,” and up-and-comers like M5 fiber armor were capturing imaginations. 

Today, given improvements in UHMWPE fiber processing, it’s stronger than Zylon ever was. It’s also very difficult to see how it can be surpassed by M5 fiber—for although M5 is stronger, it’s also much denser, and its performance would likely prove inferior to UHMWPE on an equal-weight basis. 

The list of potential near-future competitors to UHMWPE is very short. It consists primarily of nanomaterials such as carbon nanotubes and graphene, upgraded derivatives of aramid with altered chemical structures, stabilized derivatives of Zylon, and a few less likely fibers such as silk derived from genetically engineered silkworms. 

Let’s explore several of these possible options:

Carbon nanotube fibers

An electron microscope image of carbon fiber nanotubes.

Carbon fiber nanotubes armor and future helmets & armor

Armor derived from carbon nanotubes and graphene are unlikely to emerge any time soon, so I don't think it will compete with UHMWPE in the near future. 

For ballistic applications, they’d have to be very large—carbon nanotubes, for instance, would need to be many inches long—and they'd also need to be substantially free of defects. (They would therefore be, in effect, carbon fibers of the finest and highest-quality type.) 

Nanomaterial production technologies just aren't there yet. In fact, they're nowhere close.

So, while armor made of woven nanotubes is very interesting in theory—with new academic papers like this one published on the subject with some regularity—it will surely be a very long time before that theory becomes practice.

Aramid derivatives

Aramid derivatives are sometimes discussed as a potential high-performance alternative to UHMWPE.

Up until very recently, the Russian producer Kamenskvolokno was in the business of producing extremely high-grade ‘aramid.’ It was actually a modified compound that resembled, but was not identical to, the material that the rest of the world calls aramid. This material performed much better than DuPont's KM2 and Teijin's Twaron in ballistic experiments conducted by the US Army’s PEO Soldier. 

This Russian aramid derivative apparently performs almost as well as mid-grade UHMWPE. But "almost" isn't "superior," and there's little chance that any new grade of aramid will come close to beating the best grades of UHMWPE on performance. (Kevlar® EXO™ has recently been released, so it may soon be put to the test. But as of this writing, there are few publicly available details on Kevlar EXO’s performance.)

Zylon chemical structure

The chemical structure of Zylon®.

Zylon fiber ballistic protection

Zylon® (poly(p-phenylene-2,6-benzobisoxazole, or PBO) is an interesting case. Unlike carbon nanomaterials, Zylon fibers are fairly easy to make. And unlike aramids, they can potentially beat UHMWPE on performance. 

The problem with Zylon fiber armor is that it’s unstable and subject to degradation in normal heat and humidity. It’s theoretically possible to stabilize the material by altering its chemistry or applying a barrier coating during manufacturing. This could result in a very attractive fiber material for armor composites. 

But stabilized Zylon is unlikely to ever come about, for it is explicitly banned in most armor products after some police vests failed and questions about the material’s degradation sparked a recall and government action.

If you're an armor company and want to bid on a military project, you'll quickly find that most solicitations ban Zylon by name. The last one I saw required a “written declaration by the manufacturer that the Zylon anti-ballistic material (IUPAC name: poly(p-phenylene-2,6-benzobisoxazole)) or any other material, based on the same category of materials, has not been used.” 

The National Institute of Justice (NIJ), the Department of Justice’s research arm and provider of nationally accepted standards for ballistic protection, also refuses to certify any product containing it. So even if a Zylon fiber derivative could be stabilized, and even if it performs better than UHMWPE, such material would face almost insurmountable challenges in the market.

M5 Fiber chemical structure

The chemical structure of M5 fiber. Image source: Body Armor News

M5 fiber armor and helmets

M5 fiber, structurally similar to Zylon in certain respects, has an outside chance of competing with UHMWPE. But it doesn't seem that serious development work on this polymer material is ongoing, perhaps due to production difficulties or a limited non-military market for M5 fiber armor. (As a high-stiffness fiber, it competes with much cheaper carbon fiber in non-military applications.)  

And it’s unlikely, in any case, that M5 fiber armor or helmets can outperform UHMWPE; for the material is considerably denser—at 1.7 gm/cc, nearly twice as dense. And, by all projections, even the best grades of M5 would have a substantially lower specific tensile strength than the best modern grades of UHMWPE fiber. 

Those “best” grades of M5 are mere speculation; in reality, the material might not perform that well.

Future helmets and UHMWPE armor will benefit from manufacturing advancements

So, for now, and until the carbon nanomaterial guys get their act together, UHMWPE’s status as the high-end armor fiber of choice seems entrenched. Where does it go from here, and how can it cement its position? 

Perhaps most obviously, improved fiber production techniques will bring UHMWPE even closer to its theoretical strength. This effort simply represents the continuation of an ongoing process begun decades ago.

Unlike aramid—where Kevlar-29, Kevlar KM2, and Kevlar KM2+ are separated by decades—new and meaningfully improved grades of Dyneema and Spectra Shield UHMWPE are released fairly regularly, with even more advanced grades now on the horizon. This trend doesn’t appear to be slowing down with time.

As all of the UHMWPE used in armor is used in composite form, there’s another potential avenue for improvement in resin chemistry. Performance gets better whenever polyurea, polyolefin, and polystyrene resins get tougher or stronger. But, more interestingly, other resin types may also see some use.

Polysulfide—which is extremely tough, flexible, and ductile—might see use in ballistic UHMWPE composites where deformation resistance is not a design priority, such as shields and barriers. Epoxy is generally considered too stiff and brittle for ballistic applications. But new semi-ductile grades may challenge that assumption and find use in UHMWPE composites where rigidity and deformation control are essential, such as helmets. 

And it’s not just about the fibers and the resin systems considered separately; there’s plenty of work to be done on how they interface with each other. UHMWPE is a famously “slick” material, and resins don’t tend to bond well to it. This is unfortunate because, all else being equal, an increased resin-fiber bond strength improves every functional property of a fiber composite system—from the composite’s strength to its kinetic energy absorption to its rigidity and deformation resistance. 

Bonding, however, is strongly influenced by fiber surface roughness and other surface characteristics. And treatments that involve roughening UHMWPE fibers with femtosecond lasers or plasma-based techniques have shown promise in strengthening composite materials. The small reduction in fiber quality is more than offset by a much-improved bond strength between UHMWPE and its resin matrix. These techniques are still being researched and have not yet been commercialized, but the time seems very near.

Hard Head Veterans ATE helmet shell

Hard Head Veterans' UHMWPE & aramid Ballistic Helmet ATE® Lite Shell.

Ultimately, there isn't going to be a revolutionary shift in the performance or properties of UHMWPE ballistic composites. Rather, it will be a process of incremental evolution as fibers get better, resins become stronger, and tighter bonds form at the resin-fiber interface.

These technological advances, coupled with UHMWPE's widespread acceptance and use, mean this material should be around—and improving—for a long time.

Jake Ganor is the chemist and ballistics researcher behind Adept Armor, a developer of leading-edge body armor products and materials. If you enjoyed this article, you might also enjoy his book, Body Armor and Light Armor Materials and Systems.

Hard Head Veterans stays on top of helmet research to ensure we provide the best protection possible. Read more blog posts, and be sure to check out our gear, including a selection of the best tactical helmets and essential helmet accessories.