How UHMWPE Sheets Are Made into Ballistic Helmet Shells

Producing fiber-composite ballistic helmets is no simple matter. The ultra-high molecular weight polyethylene and other materials are inherently expensive, and the processing methods used to turn flat UHMWPE sheets into a finished helmet shell are complex and unforgiving. 

Aramid helmets cost the military a few orders of magnitude more than the old M1 steel pots when the former was first introduced. And aramid is both cheaper and easier to work with than UHMWPE fabric. When the military later introduced the UHMWPE-based Enhanced Combat Helmet (ECH), it cost three times as much as the aramid Advanced Combat Helmet (ACH). 

The complexity of making ballistic helmet shells generally stems from the fact that fiber composite sheets can’t easily be pressed into shape. When manufacturers attempt this approach, the result is almost always wrinkled and uneven. The UHMWPE material can’t be used or even recycled—it has to be trashed.

Note the fabric’s wrinkling on the sides of the helmet. Image source: Dangora, Lisa & Mitchell, Cynthia & Sherwood, James & Parker, Jason. (2016). “Deep-Draw Forming Trials on a Cross-ply Thermoplastic Lamina for Helmet Preform Manufacture.” Journal of Manufacturing Science and Engineering

Techniques for making UHMWPE fabric into effective ballistic protection

The most common way of sidestepping wrinkling and wasted UHMWPE material involves cutting fabric or fiber composite sheets into darted pinwheel patterns and then laying them up to distribute the seams evenly.

This pinwheel method is very effective at reducing wrinkling and waste, but not without its problems. It's very obviously labor-intensive, for one thing. For another, the seams themselves reduce ballistic performance. This issue is partly why body armor plates and soft armor panels outperform helmets at equal weight and thickness.

An interesting side-effect of this process is that the crown of the helmet—which is seamless—is considerably stronger than the front, sides, and rear. This can safely be considered a negative side-effect because the crown is least likely to be struck by a high-velocity projectile.

Common fiber-cutting patterns. Image source: Dangora, Lisa & Mitchell, Cynthia & Sherwood, James & Parker, Jason. (2016). “Deep-Draw Forming Trials on a Cross-ply Thermoplastic Lamina for Helmet Preform Manufacture.” Journal of Manufacturing Science and Engineering

After fiber composite sheets are pinwheel-darted and laid up properly, manufacturers consolidate them under heat and pressure. This generally takes place in a matched-metal or silicone mold at an elevated temperature, in a process that typically takes 20 minutes from start to finish. When the semi-finished helmet shells come out of the mold, they’re trimmed and painted, and edge trim is applied. Then the headgear is ready for pads and a retention system.

This process is how Kevlar® headgear has been made for nearly 50 years, with minimal variation between manufacturers. It has enabled the industrial production of aramid helmets on massive scales—millions of them have been built in this manner. It’s also how many UHMWPE helmets are made today.

UHMWPE sheets present novel manufacturing challenges

UHMWPE adds several points of added complexity when building ballistic helmets. First, it degrades at elevated temperatures. So, although all consolidation processes employ heat, they run at relatively cool temperatures with UHMWPE materials—often a hundred degrees cooler than the temperatures used to produce aramid gear. 

Second, end-users are beginning to demand superior ballistic performance from their UHMWPE helmets —including, in many cases, the ability to stop direct hits from rifle rounds. So, the pinwheel method is quickly falling out of favor due to the reduced ballistic performance when products are constructed via that method. 

UHMWPE ballistic helmets can be manufactured via non-pinwheel means, but such methods are often exotic and proprietary. 

Deep drawing and other manufacturing techniques using UHMWPE sheets 

One way to create a UHMWPE helmet without pinwheeling is called “deep drawing.” It involves drawing a UHMWPE composite through a die via a punch with the assistance of binders. Done properly—and there’s a steep learning curve—the process can result in a helmet that’s free of both wrinkles and internal seams. The major issue is UHMWPE material waste, which can be considerable. 

Compared with the pinwheel method, there's also a curious counter-phenomenon: Because all the pressure is applied to the crown, a “deep drawn” UHMWPE helmet’s top is perhaps the weakest and most stretched-out part on the helmet shell. There can also be resin flow from the crown to the sides of the headgear, resulting in variable helmet shell thickness.

Deep drawing method for making ballistic helmet shells

An illustration of the deep drawing method for making UHMWPE ballistic helmet shells.

Other known approaches involve high-pressure autoclaves, multi-stage deep-drawing processes, or hydroclaves. Ultimately, every method boils down to the same thing: applying heat (as little as possible) and pressure (as much as possible) to press flat UHMWPE sheets into a resin-bound helmet geometry without pinwheeling, seams, wrinkles, grossly variable helmet shell thickness, or any other structural features that would reduce ballistic performance or make it inconsistent. 

Additional materials may be used to reinforce or stiffen the shell, but they’re ancillary and usually fairly easy to work with. Carbon fiber is, by a wide margin, the most common reinforcing material, and it’s famously easy to form into complex geometries.   

Ballistic helmet shell advances are starting to catch up with UHMWPE armor

By 2009, lightweight all-polymer armor plates capable of protecting against rifle rounds were commonplace. Just a few years later, with the ECH, lightweight UHMWPE-based helmets began to offer similar, if slightly reduced, performance. And today, we're starting to see headgear that’s competitive with armor plates on a performance-to-weight basis. 

The technologies that enable this capability go beyond UHMWPE fibers and supporting resins; high-pressure, low-temperature, seamless helmet shell consolidation methods have everything to do with it.

Read part four of this series, where we dive into the future of helmets and armor, exploring whether any materials will replaced UHMWPE.

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.