Light armors are used to protect people against light weapons for military and nonmilitary purposes such as protecting police and civilians against criminals or protecting people even in hunting. Today, they are usually manufactured from polymer matrix composites due to their high stiffness/weight ratio. The good ballistic property means the measure of absorbability of the kinetic energy of a bullet or projectile without any major injury on the person. Designing the armor for only penetration is not enough for protection. The backside deformation of the armor must be also investigated because the projectile can produce not only bruises and lacerations of the surface of the skin, but can also damage internal organs. In this study, the backside deformation is determined experimentally and analytically for Kevlar 29/Polivnyl Butyral and Polyethylene fiber composites.