I am thinking to build a bullet proof vest with steel plates. For vest number 1, I'm thinking use either use a 7mm plate. For vest number 2 I'm thinking to use a 4mm plate + some material + a 3mm plate. "Some material" could be either options such as aluminium foil, 1 layer of kevlar 29 or something else (feel free to suggest).
I wonder, which vest would perform better in terms of preventing bullets to go through? do you think any of them has more chance to stop a NATO 5.56 bullet…

Is two-plate armor better than a one-plate one with the same overall thickness?