For next generation of miniaturized personal electronics and pulsed power systems for smart power grids, electric vehicles, and electromagnetic launchers, flexible capacitors from dielectric polymers with high-capacity, high-efficiency, and fast response are highly desirable. Dielectric polymer composite of P(VDF-CTFE), that is poly(vinylidene fluoride-chlorotrifluoroethylene) and a small amount of aromatic polythiourea (PTU) has been described. It combines the merits of both polymers, that is high dipole density and easy processability of P(VDF-CTFE), as well as large dipole moment and high charge-discharge efficiency of PTU. Most impressively, PTU boosts the maximum breakdown strength of P(VDF-CTFE), and thus extracts its maximum energy reserve capacity. PTU also contributes to the promoted charge-discharge efficiency, accelerated discharge, and reduced dielectric loss in P(VDF-CTFE), which facilitate the composite for flexible capacitor applications. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 193-199