In this study, a sticky copolymer of water-born polyurethane-potassium poly(acrylate) (WPU-PAAK) is designed for acting as not only a gel electrolyte but also a binder in manufacturing the carbon-based electrodes for flexible, quasi solid-state electrical double-layer capacitors (EDLCs). This copolymer has been successfully synthesized from potassium poly(acrylate) backbone cross-linked with water-born polyurethane. In comparison with the most common poly(vinylidene fluoride) (PVDF) binder, WPU-PAAK enhances the areal specific capacitance of activated carbon/carbon nanotube (AC/CNT)-coated electrode about 64% and over 100% at 1 and 10 mA cm(-2), respectively. More importantly, the areal specific capacitance of AC/CNT composites with the WPU-PAAK binder is directly proportional to their mass loading, revealing the perfect utilization of active materials. The quasi solid-state device of the sandwich type demonstrates a potential window of 1.4 V and a high device-areal specific capacitance of 122.43 mF cm(-2) at 1 mA cm(-2). This highly flexible electrical double-layer capacitor (over 95.6% areal specific capacitance retention at a bending angle of 180) also delivers an energy density of 33.33 mu Wh cm(-2) at a power density of 0.7 mW cm(-2) with an excellent cycle life of 87.5% retention in the 10,000-cycle test.