The interphases of various sized E-glass-®ber/epoxy-amine systems were tested at displacement rates in the range 230±2450 mm/s by a new experimental technique (dynamic micro-debonding technique). By this method, the rate-dependent interphase properties, apparent shear strength and absorbed energies due to debonding and frictional sliding, were quanti®ed. The systems include unsized, epoxy-amine compatible, and epoxy-amine incompatible glass ®bers. The high displacement rates that induce high-strain-rate interphase loading were obtained by using the rapid expansion capability of piezoelectric actuators (PZT). The results of dynamic micro-debonding experiments showed that the values of interphase strength and speci®c absorbed energies varied in a manner that is dependent on the sizing and exhibited signi®cant sensitivity to loading rates. The unsized ®bers exhibit greater frictional sliding energies that could provide better ballistic resistance, while the compatible sized ®bers show higher strength values that improve the structural integrity of the polymeric composites. In addition, signi®cantly higher amounts of energy are absorbed within the frictional sliding regime compared to debonding. By using the experimental data obtained, a case study was performed to reveal the importance of the interphase related micro damage modes on energy absorption (and therefore ballistic performance)of glass/epoxy composite armor