Roamy here. Five or so years ago, there were several brands of bullet-proof vests that were pulled off the market because of a common material that started losing its strength. At that same time, I was testing the same material, Zylon, for use in space tethers. I was finding out what the Justice Department ballistics people had already found out – that Zylon loses strength when exposed to sunlight and also humidity. Reports were that Zylon was losing 10% to 20% of its original strength, so all the advantages of being lighter weight than Kevlar went right out the window. I was seeing even more than that with the more intense ultraviolet radiation, simulating space.
No one likes having an expiration date on their bulletproof vest, so the inevitable lawsuits followed and were settled last year and earlier this year. Space tether studies went on to new materials. (Lest you think space tethers are a new thing, they actually date back to Gemini 11 in 1966.)
XBrad can correct me on this, but bulletproof vests these days are mostly aramid materials – Kevlar, Nomex, Twaron, and the like. Next post, I’ll talk about how the development of bulletproof vests led to better shielding for the International Space Station.