Materials of Body Armor
In our previous two articles, SSE covered the various types of body armor, and the National Institute of Justice as it relates to that agency’s ballistic testing and rating system. The purpose of this, the third in a series of publications on body armor, is to introduce to the reader to the various materials used in the manufacture of body armor, the characteristics of each, and overall curvature.
Materials in body armor have evolved over time and with technology. Yet today some are more traditional while others are pushing the edge of current science. They can also range from the inexpensive, to very. Following this scale, the dominant material used for body armor today includes:
1. AR500/550/650 Steel
Made from extruded raw sheets of steel, ARXXX body armor is by far the most inexpensive. The name of AR500 steel refers to its “abrasion resistance” and its 500/550/650 Brinell Hardness rating. The Brinell rating is used to rate the hardness of steel and various other materials. The higher the Brinell rating, the harder the steel. Higher Brinell ratings also translates to faster velocities and heavier caliber of rounds defeated, without penetrating the plate or going beyond the maximum acceptable indentation or deformation. For AR500 steel, the National Institute of Justice has set a deformation maximum of 44 millimeters. So really with steel plates, it comes down to a matter of physics—is the density of the steel greater than that of the projectile striking it, and is it sufficient to cause said projectile to shatter on impact.
But steel plates do have their drawbacks, specifically spall (otherwise thought of as the shrapnel of the impacted round as it strikes the steel and fragments outward). This spall can cause deep lacerations to yourself or others around you if not properly mitigated, and even then much of today’s anti-fragmentary coatings will only work for so long before the spall completely delaminates and defeats the coating. Other drawbacks to steel plates are that while it is the most affordable, it is also the heaviest. Steel is more frequently used to make targets, and because steel isn’t rated to stop most high velocity 5.56 (3200fps) it can be easily penetrated. The only steel used that can stop high velocity projectiles is Mil-Spec A46100, a material frequently used in military vehicles and not feasible for individual wear.
Kevlar is another traditional material discovered by the DuPont company and used in the manufacture of PPE. Today Kevlar is perhaps the most common aramid used in everything from body armor, transportation, aircraft, and even the space shuttle. The molecular bonds inside the Kevlar are extremely strong due to how those molecules are arranged. As Kevlar starts out, it is a thin, watery liquid, but as it hardens, it forms very tight chemical bonds between the molecules – thus it is body armor at the molecular level. Those threads are then woven into a soft, flexible material to form the multiple layers of body armor. How Kevlar defeats a projectile is that in essence, the object is forced to expend all of its kinetic energy as it attempts to push through the dense Kevlar fibers. One of the most pronounced drawbacks to Kevlar is that over time and exposure the individual strands can become brittle and deteriorate, thus making the body armor compromised. Proper storage of Kevlar soft armor is to lay it flat on a shelf or other such surface. In addition, kevlar is also heavier than most aramids and retains moisture in its unconsolidated form.
By far ceramic is the most common type of material used in today’s manufacture of body armor. Today’s ceramics are frequently made from alumina, boron carbide, silicon carbide, and titanium diboride. The intent behind ceramic body armor is that it offers a high degree of hardness, with compressive strength that contains the projectile fragments after it strikes the surface and shatters, with little of the back force deformation experienced with steel. Furthermore, ceramics are significantly lighter than steel and incorporate a backer or outer composite layer for added protection and structure. This makes ceramic plates ideal for defeating 5.56 rifle caliber ammunition.
The downside to ceramic body armor is that many plates cannot withstand multiple direct hits at the exact same point of impact. As technology in ceramics has improved, so has the durability to withstand multiple hits. And while the odds of you being struck exactly at the same point of impact multiple times is exceedingly rare, the point of ceramic is that it fractures/cracks. Some vendors use hybrid materials, coatings, wraps to help keep the ceramic plates intact despite being cracked, thus retaining some multi-hit factor—but this still doesn’t change the compromised material at the point of impact.
4. “Specialty” Materials
There are obviously, a number of exotic or “specialty” type materials that are also used to manufacture body armor. The principle components to this are highly resistant versions of polyethylene – a type of plastic. The first of these specialty materials is Ultra-High Molecular Weight Polyethylene (UHMWPE), which is a subset of thermoplastic polyethylene, and has the highest impact strength of any thermoplastic currently on the market. As a material, UHMWPE has outstanding physical and mechanical properties, including chemical inertness, self-lubricity, impact resistance, and abrasion resistance—it can even float! To produce, thin sheets of UHMWPE are heat-laminated together under high pressure until they bond into one striated composite piece. That layered structure compounds the individual layer’s impact resistance, resulting in greater strength. The principle effect then is that as a projectile strikes UHMWPE plates, it’s energy super-heats the polyethylene to melt around the projectile and immediately harden, thus capturing the projectile. But the one crux to UHMWPE is steel-core ammunition (like M855), which easily passes through pure UHMWPE plates, almost like a sabot round fired from a tank. Manufacturers can offset UHMWPE plates by making the plates a hybrid construction by including a backer or additional plate layer to defeat steel-core ammunition (usually under the “+” identifier), but the tradeoff is at the expense of more weight.
The other widely used specialty material is a patented polyethylene product called “Duritium” and made from an advanced UHMWPE chemical composition. Duritium is a patented blend of material by the company ShotStop, and the company claims Duritium offers 30% reduction in thickness and weight, while maintaining a Level III protection value. The same disadvantages of UHMWPE are shared by Duritium, but again manufacturers offset this by adding additional materials to defeat those threats under the “+” identifier.
However, as exploratory tests in July 2021 of samples taken from ShotStop’s Level III and IV line have revealed, the plates by ShotStop are not full “edge-to-edge” protection, but rather have a 1.0″-1.75″ Styrofoam padding (the exclusion to this was found to be the full polyethylene buffer found in the Level III+ PA model). This feature (sometimes referred to as a buffer or bump) helps minimize the weight, but this is something that isn’t disclosed in the ShotStop product descriptions. This means that the plates can have a protective ceramic core (the part that actually stops/breaks up the bullet that is sometimes referred to as an “effective coverage” area) up to nearly three inches less than the customer thinks they are getting. And while ShotStop discusses “less than full body coverage” in a separate blog post, the article avoids disclosing how much of ShotStop’s products lack full edge-to-edge torso coverage. Clever marketing strategies such as this are made possible because NIJ testing mandates its ballistic testing has to be done within 2″ away from the edges, and from each consecutive shot. So some companies play that requirement to their advantage by offering diminished protective profiles wrapped in a buffer that cannot be distinguished from the exterior, but would still fall within the testing parameters of the NIJ.
5. Spall Coating
Another type of material used in the manufacturer of steel body armor is spall coating. As noted above, spall coating is a soft, thicker polyurea layer (think liquid truck bed liner) intended to absorb and contain bullet fragmentation/spalling, and thus prevent the end-user from being injured. However, repeated shots on steel plates with spall coating will eventually result in delamination, as the spall slices between the denser steel’s outer surface and the weaker inner layer of polyurea. Yes, multiple layers of spall coating will increase the protection value, making it thicker and thus harder for spall to cut through. But eventually, as anyone who has spent time on the range will tell you by looking at the target stands or support structures to steel targets…eventually the fragmentation will slice through and penetrate into the supportive materials – be it wood or flesh.
Lastly, the curvature of ballistic plates has expanded well beyond a linear plane of protective material (although you can still purchase flat panels). Such curvature is often done to enhance the ergonomics of the ballistic plate and improve comfort over long-term wear. Forming the curvature is based on the material and done via mold compression (for Kevlar or ceramic), or press (for steel). Caution needs to be exercised by the manufacturer during the bending process however, because done inappropriately or too forcefully can result in a crease or render the batch unusable. Single curve body armor has a single bend (typically vertically) to wrap around the torso for a generalized fit. Multi-curve SAPI/ESAPI body armor has six angled curves that give the plate a much more anatomical and specific fit. A European-centric curvature exists called “triple curve”, and indeed has three curves to it, but it is not as popular in American markets.
Disclaimer: The purpose of this PPE series is strictly informational, much like our COVID Chronicles on plate carriers, this series is not intended by SSE to sway or convince the reader that one specific brand of body armor is superior to all the others. In the end, this series is intended to provide the reader with a condensed and focused resource—nothing more. As always, check with your local laws as some states have regulations on ownership of body armor by civilians.
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