Engineering360: "Engineers improve material used in bullet-proof gear"

I think that you mean invulnerability. You are talking about improving the vest thru materials science.

vul·ner·a·bil·i·ty Learn to pronounce noun

1. the quality or state of being exposed to the possibility of being attacked or harmed, either physically or emotionally.

Definition of invulnerable. 1 : incapable of being wounded, injured, or harmed. 2 : immune to or proof against attack : impregnable.