And so it was that a great need was upon the land. With projectiles achieving higher velocities, and greater penetration, Nylon just was not cutting the mustard. Even though it excelled silk for use in soft armor, it still lacked the requisite tensile strength to stop modern copper jacketed handgun rounds in anything approaching wearable ADs.
In 1965, a Dupont chemist named Stephanie Kwolek stumbled upon a new material while searching for alternatives to steel in tire reinforcements. This new material had a tensile strength 5 times that of steel on an equal weight basis. The structure resembled natural silk, but what made Kevlar outstanding was the propensity for the fibers to form cross-linked hydrogen bonds at 90 degrees to the polymer chain. This gave the new fiber exceptional tenacity, making it ideally suited for use in ballistic armor.
This, combined with excellent heat and flame resistance (Aramid fibers do not burn, they char at around 700 F), lead to a resurgence in concealable personal body armor. Richard Davies, founder of Second Chance, immediately saw the potential of this fiber, and the modern “bulletproof vest” was born.
Kevlar is the trade name for aramid fiber developed by Dupont, but there are several different brands of aramid fiber, including Teijin’s Twaron. Though originally discovered by Dupont, Teijin, a Netherlands based company, perfected and patented an aramid fiber processing method that Dupont later licensed to use themselves. Whether we are talking about Kevlar aramid or Twaron aramid, the properties are very similar.
To this day, aramid is widely used in armor applications. During the 70’s and 80’s, the only form used was woven fabric, cut and layered up to 35 plies deep. In the 90’s, new iterations of bullet resistant composites were brought to market, including laminates.
Laminates were introduced in search of the ever moving goal post of thinner and lighter armor. Of course, as has been the case throughout history, heavy and cumbersome armor is not fun to wear. To get folks to wear their armor, thin and light make sense. However, as will be seen, laminates were not necessarily better, and could even be seen as a step backwards (at least the first and second generation iterations).
Laminates such as Goldflex and Gold Shield utilize polypropylene films (chemically similar to food preservative film) to sandwich unidirectional aramid fibers in alternating 0 degree and 90 degree layers. Admittedly, this results in a very good material for stopping bullets, including hits near the edge of a panel, and at acute angles to the panel.
Unfortunately, several drawbacks rear their ugly heads with aramid laminates. First off, they have the breatheability of plastic wrap. Which is zero, since similar materials are used as vapor barriers. Secondly, the plastic film has a nasty tendency to melt when the panel is subjected to the hot muzzle blast of contact shots (an event all-to common in the course of law enforcement). In contrast, woven aramid is extremely effective at resisting contact shots. Finally, armor made with first and second generation laminates experience accelerated wear, since the adhesion of the film is degraded by repeated exposure to flexing, heat, cold and moisture.
While an armor built with woven aramid could reasonably be expected to survive (and remain fully effective!) for over 25 years (and I have personally verified that they HAVE), a laminate constructed armor is usually toast after only two years of normal wear. The edges curl, the layers peel apart, and the ballistic effectiveness drops to unsafe levels. In much the same way that a chain is only as strong as its weakest link, first and second generation laminates are hobbled by their use of, essentially, plastic wrap in their construction.
Next episode, we will look at another laminate, one that has great numbers, but hidden dangers…
d-rmor gear 