Body Armor: The Good, The Bad, and The Ugly, Part III

Posted: March 3, 2014 in Body Armor The Good The Bad and The Ugly
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In the late 80’s and early 90’s a relatively new material was making an appearance in concealable body armor. Based on the Ultra High Molecular Weight Polyethylene molecule, this material offered tensile strength 8-15 times that of steel on a weight-to-weight basis. This was up to 40% higher than Aramid fiber. Developed by DSM, this material became known by two different trade names, Dyneema (DSM) and Spectra (Honeywell). Initially, this material was utilized as both a woven panel (which had immediate problems, as will be discussed below), and later in a laminate form (called Shield technology, similar to Gold Shield aramid laminate).

In the same way that aramid laminates utilized a poly-film matrix, so too did Dyneema and Spectra laminates. The UHMWPE fibers in laminate armor materials are unidirectional (all running in the same direction) and offset by 90 degrees in each successive layer. While this material, which is still widely used in soft armor, has impressive performance (much lower AD than aramid based armors, no UV susceptibility, positive buoyancy), there are fatal flaws that an end-user must be made aware of.

In addition to having the drawbacks of aramid laminates (de-lamination/peeling, extremely poor breateability), UHMWPE laminates also suffer from heat sensitivity. The UHMWPE molecule is chemically similar to garden-variety Polyethylene (the same material used in plastic milk jugs). When Spectra or Dyneema is exposed to temperatures above 170 Degrees F, it permanently and irreversibly denatures/reverts to the same milk-jug plastic (which has absolutely NO ballistic properties at all).

Because armor is often exposed to a wide range of temperatures (for example, in many parts of the country, a car trunk/interior can easily reach 180-190 F), this is a major concern. Furthermore, since there is no visible change to the material, there is no way for the end user to know if their armor is still viable, or merely layers of coffee can lid. Originally, woven UHMWPE armors were produced (called Spectraflex), but since the higher surface area of the woven fibers made the armor even more prone to heat degradation (a hot cup of coffee, for instance, would have a greater effect on a woven UHMWPE vest compared to a laminate, due to the vapor/moisture barrier properties of the laminate), they were quickly withdrawn from the market.

In addition, Spectra/Dyneema based armors fare poorly in situations where they may be subjected to contact shots- the hot muzzle blast gasses can melt the armor around the impact area, allowing the bullet to penetrate more layers (sometimes even the entire vest) than would have been possible with a woven aramid based vest. All laminates suffer poor contact shot resistance, but UHMWPE is especially susceptible. I will be dedicating a post on contact shots in the coming months.

What does all this mean for you, the end user? First of all, it is vital to identify armor containing UHMWPE, and to a similar extent, first and second generation laminates (I will be posting a tutorial on armor material identification in the coming months). If you are able to assess your needs prior to purchasing armor, ask yourself if you will be operating in environments that expose the weaknesses of UHMWPE or laminates (potential for elevated temperatures, likelihood of contact shots, requirement for high exertion/perspiration). If none of these circumstances are likely to be encountered, the dangers of UHMWPE/Laminates will be minimized. But if one or more apply, it is strongly recommended you find an armor system consisting of 100% WOVEN ARAMID.

It is important to note that this applies only to soft armor. UHMWPE/Spectra/Dyneema/Aramid Laminates find extensive use in hard/rigid armors (both as a pure defense and as backing material for the strike face. This will be discussed in a later post, but for now, please note that evidence strongly suggests in a rigid configuration, UHMWPE/Laminates do not exhibit the same dangers/weaknesses as when utilized in soft armor.

Next: The most dangerous (to the wearer) soft armor material. Stay tuned.


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