AT Armor released a graphic (below) that shows how their STOP plates work to defeat projectiles. Ballistic armor is amazing to me and it is staggering to think about how many lives it has saved. You would think it would be more complicated but the graphic shows just how simple the mechanics of stopping a bullet are (the materials necessary to make a plate as thin and light as the STOP plates are anything but simple).
From AT Armor:
AT Armor’s STOP and STOP-BZ plates are multi-component (aka hybrid) construction that defeat multiple hits of rated projectiles with a ceramic strike face and a subsequent layer of high-pressure compressed ballistic material. The advantage of our STOP series armor is it is very light (as light as 4lbs stand alone in a Med SAPI) and it is thin (.55 inches). Fully capable against common 5.56 threats and 7.62×39 mild steel and AP (STOP-BZ plate).
Check out the STOP Plates at AT Armor.