Anyone interested in this subject should go Glocktalk.com and read the long history about this.
Basic story is Fed testing standards did not include moisture and heat related degradation tests.
Zylon degrades very much faster than other "blended" weaves when subjected to heat and moisture extremes.
There have been several failures/officers killed when zylon vests failed way before (read a year or less from manufacture) the 5 year expected life span was up.
Second Chance's in house scientist/engineer found this through his testing and was shut down by the company because (even though the vests were failing) "they met the standard."
You will see most failures have occurred in hot and or humid climates. Think CA/AZ.
Coincidently about the time Second Chance was denying internally that they had a problem with Zylon they were going public.
Now they are bankrupt and have been bought out.