In this world, there are a small percentage of humans with "special" abilities. The source of these abilities is alien genetic meddling for their own cryptic reasons (though the characters don't know it yet) so evolution is not a point there. The time frame (for technology levels) would be present day.
I'd like for one of these abilities to be the ability to quickly grow a sort of organic body armor (the need for that ability has a reason in-story), not necessary for all the body (for example, they could grow only vambraces or similar). The armor would grow/appear when needed (in combat situations, for example) and, once the danger has passed, the armor would either molt or be reabsorbed by the body.
What I'm more interested is in the composition of the armor itself. The armor should be puncture and bullet-proof, at least with regular weapons (armor-piercing weapons may exist but be expensive). It will be great if it could be some sort of anti-conductive or reflecting properties to give some protection against energy-based weapons (that the characters encounter later).
Initially, I was thinking in something made of keratin or keratin-like substance (chitin? spider silk?) that might work similarly to current-day bulletproof vests, so even if the armor blocks a bullet, the flesh within may get bruised. Then I thought about some kind of organic polymer with viscoelastic properties or something similar.
I know I'm getting more into X-Men territory, but is there any way something like that might be somewhat plausible? Or at least plausible enough for my readers to suspend belief and keep reading and not just roll their eyes and throw my story to the wastebasket. My story is more soft SF than hard SF, but I'd like some believability.
Please, take into account that I'm an historian, not a chemist or physicist. Thank you!