Why do fencers wear metal vests?
Metallic vests are for competition. You may notice that the fencer will also have a cable tied to the back of their vest. These vests are used to help keep score. In foil competition, the torso is the only valid target, so a metallic vest is worn over the torso. When a touch on the vest is scored by the opponent, a circuit is opened (or closed, I forget) and that signals the electronic scoring system to score a touch. Because the blades are often moving extremely quickly, this system is much more accurate than having a judge determine which touches are valid.
