Fibrous electrochemical capacitors (FECs) with outstanding wearability, mechanical properties and satisfactorily high energy density are greatly required for developing wearable smart devices and sustainable energy sources. Herein, new high performance FECs based on flexible but insulating aramid fibres (KFs) were developed through chemically grafting composite coatings of Ag nanoparticles, carbon nanotubes (CNTs) and capacitive polypyrrole (PPy), successively. Their structures and integrated performances were intensively studied. The PPy loading plays an important role on the capacitive properties of new KFs, and there is an optimum content of PPy for getting the best integrated performances. It is interesting to find that the capacitive property of KF/Ag/CNT/PPy is not the simple combination but much higher than those of KF/Ag/PPy and KF/CNT/PPy, proving that there is a synergistic effect between Ag and CNT coatings. This synergistic effect endows KF/Ag/CNT/PPy fibres with high specific capacitance and large energy density. For example, the specific capacitance and energy density of the novel aramid fibre capacitor with the optimum content of PPy (KF/Ag/CNT/PPy0.2) are as high as 84.3 F cm(-3) (or 24.8 F g(-1)) and 7.49 m Wh cm(-3) (or 2.21 mW h g(-1)), respectively. In addition, KF/Ag/CNT/PPy0.2 exhibits enhanced cyclability and wearability (its capacitance retains 94.0% after 1000 cycles and 93.2% after bending for 500 times) because of the special design of strong interactions between different components. Note that KF/Ag/CNT/PPy0.2 also has high tensile strength, modulus and break extension. These attractive integrated performances demonstrate that KF/Ag/CNT/PPy0.2 makes obvious breakthrough on developing FECs based on polymer fibres, and thus have great prospect in fabricating wearable electronic devices and sustainable energy sources. (C) 2018 Elsevier Ltd. All rights reserved.