Below was posted in response to some questions about body armor:
First off- avoid Spectrashield, Spectra woven, or Dyneema: This material is based on polyethylene, the same stuff that milk jugs are made of. The armor version is referred to as Ultra High Molecular Weight Poly-Ethylene (UHMWPE). In situations where it gets hot (and most car trunks in the summer can get HOT), it will denature, reverting back to simple milk jug plastic. Armoring FAIL. I used to be a fan of this stuff until I read some great info by Kevin "Mad Dog" Mclung and Doctor Roberts ("DocGKR"), two names that you should look up and listen to. They did some eye opening tests (especially Mad Dog) on the dangers of Spectra. If the material goes over 180 F, it becomes a danger to its wearer.
Avoid Laminates: Something else both of these gentlemen strongly advise against. Laminated armor materials have huge drawbacks (Spectra laminates more so). They suck against contact shots (the muzzle blast literally melts them, allowing rounds to go right through), they delaminate with wear, they don't breathe (try wrapping yourself in saran wrap- that's how comfy they are), and they don't have anywhere near the shelf life of woven kevlar (which is practically immortal as far as I have seen). Steer clear of laminates.
AVOID ZYLON: For the love of everything that is holy. There was an amendment passed in congress outlawing this stuff for pete's sake. It was supposed to be the next great armor material, and lots of manufacturers jumped on it. Trouble is, combine heat with humidity (um, your body?) and the material degraded rapidly. This lead directly to the deaths of at least two police officers, and Zylon was (after much foot dragging) pulled. Don't ever use it.
Pretty muchly that leaves woven aramid as the last man standing. This stuff is, as always, a great material. It is tough, fireproof (it will char but not melt at above 700 F) and will retain most of its ballistic effectiveness even after reaching this temp. Being woven, it breathes better. Contact shots have a much harder time getting through. It lasts virtually forever- the 5-7 year warranty is not there to tell you when it goes bad. Nominally, it is just there as a CYA measure by the companies to limit liability. In one test, it was actually shown that older vests did BETTER than new vests at stopping rounds. Wierd, I know. Here are two references:
“NIJ tests failed to demonstrate any significant differences in 10-year-old armor, regardless of the extent of use or apparent physical condition”
“The warranty exists solely to limit the manufacturer's liability on the product and is not a reflection of the anticipated service life of the product.”
...Guide to Police Body Armor, National Law Enforcement and Corrections Technology Center (NLECTC)
You can also find an abstract here:
So kevlar, kevlar, kevlar. Woven, not laminated.
Regarding plates- Rifle armor is important, as soft armor is completely useless against rifle rounds. M193 will go through about 120-140 layers of soft armor with enough zip left to seriously ruin your weekend. Believe me, I have checked.
Just to reiterate, soft armor cannot be level III. Max rating is IIIA. And don't assume, get the specs, or better yet, test it yourself!
Rifle armor is rated either level III or IV. Now, the interesting thing is, the higher rating is not necessarily better. If you expect to be facing enemies with AP capability, the IV is nice to have (the spec calls for the plate to stop ONE round of .30-06 M2 AP black tip. One round). If you are expecting normal mild steel or lead cored, go with III by all means. The spec for III calls for stopping 6 rounds of M80 .308 ball @ 2750FPS within a 6" circle. So much better multi hit. Always read the specs!
Then there is the question whether the plate is designed to stand alone, or be worn with soft armor behind it ("In Conjunction With). The stand alone plates tend to be heavier, as they typically have much thicker backings. This is nice if you are wearing just the plates and nothing else, but usually you have some sort of soft armor on, so the ICW are usually a better bet. Plus, just me, I like having extra padding. But if (like Doc mentions) you like mobility, then stand alones might be for you.
Materials for rifle armor usually focus on hard stuff- soft armor defeats pistol rounds by catching, slowing, and deforming them. They are low velocity (relatively) with a fairly large frontal area. Rifle rounds are fast, with a small, pointed frontal area. The defeat mechanism is yawing, deforming, eroding, shattering, and frictive braking (the last one is unusual).
Steel- Tried and true, this material is great for stopping rounds (millions of steel targets can't all be wrong). It stops by deforming rounds. It can keep stopping them as long as the structure is uncompromised. Heat and mistreatment do not affect it. Drawbacks- it is heavy for its protective levels, it can rust if you chip the paint, and it spalls. What is spall? Well, it is the reason most steel target manufacturers recommend being 50-100 yards from the target. When a round hits, it splashes little bits of copper and lead in a cone at an angle. If you are wearing one of these plates, that high velocity splash can end up in your throat and face. Make sure if you run steel plates you wear spall guards in FRONT of the plates. Just a few layers of kevlar are all that is needed. One final drawback to steel plates- certain high velocity threats can penetrate it. A few years back, there was a dustup over a certain manufacturers plates not stopping M193 @ above 3000 fps (but remember, M193 is not in the spec!). So do your homework.
Titanium- Ahhh, Titanium. The very word brings to mind a supermetal that can do everything. More misconceptions surround this metal than just about any other. While true, it does make superior armor in some regards, it is not a panacea. Ti has been used for several decades in the construction of advanced airframes (the A-12 was over 60% Ti, a strategic metal mostly found in Russia...). Its claims to fame are: lightweight (60% the weight of steel @ comparable strengths) and corrosion resistance. It is virtually impervious to corrosion (ironically, because it oxidizes so quickly, forming a tough layer of TiO2). It cannot be hardened appreciably above the high 40s low 50s Rockwell C, and even that requires exotic precipitation hardening Beta alloys. The most common alloy in use is referred to as 6-4, which is short for 6Al4V (6 points of Aluminum and 4 points of Vanadium). Ti is a fairly tough metal, which makes it a good choice for armor plates for AFVs and APCs in thick section (I don't have the TE numbers compared to RHA in front of me right now, but they are pretty good). In soft armor vests, Ti plates are sought after as trauma plates vs. steel because they are lighter and do not rust. In sufficient thickness (2-3mm) they will stop all handgun rounds, up to and including some AP like the steel cored Tok rounds that play merry hob with most soft armor.
For rifle armor, Ti falls short- it is not hard enough to shatter high velocity rifle rounds (see above re: hardness). This is where the TE (thickness equivalency) comes into play. Ti can stop rifle rounds, even larger caliber cannon fire, but in thicknesses and weights that are prohibitive to us groundpounders. My research has shown M80 will be stopped by a 14mm thick plate of 6-4 backed by 4mm of Aramid. Most steel plates are between 4.5mm and 6mm depending on backing. There have been some hybrid steel/Ti plates, but at that point, you might as well just go all steel. Choose the right material for the job- for pistol rounds, Ti is a champ. For rifles, look elsewhere.
Ceramic- This material encompasses several types of ceramic. The most common is Alumina, also known as Aluminum Oxide or Al2O3. It is very hard (upwards of 9 on the Moh's hardness scale), fairly light, inert, and not TOO expensive. It stops projectiles by erosion, shattering, and yawing. It is almost never used alone, relying on a backing to keep the high velocity rubble and projectile fragments from continuing into your body cavity. It is great against lots of rifle rounds, and can be made proof against some AP rounds. It is insensitive to heat and water. Drawbacks- more expensive than steel, can be sensitive to mishandling (think cracked plates if you toss them in your gear bag). Other ceramics include Silicon Carbide and Boron Carbide (more expensive and VERY expensive respectively). These are lighter and harder materials, and can stop the very highest of threats (tungsten carbide cored AP for instance). Most level IV plates are B4C.
Spectra- Wait, didn't I just say don't use this? Yes, yes I did. I am including this here for information purposes, and also because it is a gray area. Spectra in hard armor is not as HUGE a danger as soft armor (this from DocGKR) because of the amount of heat required to get it isothermic (the same temp throughout). So, if you have Spectra hardplates, there you go. Standalone Spectra plates can stop rifle rounds with enough layers. It stops rounds via frictive braking (think of bullet brake). However, be advised there are some rounds that will penetrate UHMWPE plates, such as M855 green tip. So again, do your homework.
I hope this has been helpful- armor is one of those things that should be in everyone's kit bag.