Modern bullet-resistant body armor comes in both hard and soft varieties. Soft body armor uses layers of tightly-woven super-strong fibers like Kevlar or Spectra that disperse the kinetic energy of bullets across the vest surface, preventing penetration without concentrating impact in one area and causing injury. Hard armor incorporates rigid plates that deflect bullets through their hardness. Body armor is rated on a scale from I to IV based on the types of weapons it can withstand, with higher grades offering more protection but less flexibility.