This report explores the possibility that heat plays a role in the penetration of cloth ballistic panels by 0.22 caliber projectiles. We postulate that heat is generated by friction between the surface of the projectile and the yarns, between yarns, and between filaments within a yarn in advance of and in the path of the projectile. Evaluations by light microscopy, polarized light microscopy, and scanning electron microscopy show heat- induced damage in fibers in the path of and several layers preceding the layer at which a 0.22 caliber projectile comes to rest. Polarization microscopy of impacted yarns reveals differences in birefringence within the fibers close to the hole made by the projectile compared with the same fiber at a greater distance from the hole. Heat is an energy sink, and depending on how, when, and where it is generated, can degrade the ballistic performance of the yarns. The quantitative importance of heat in affecting ballistic panel performance is elusive: consequently, the discussion presented here is largely qualitative.