Graphene-based all-solid-state supercapacitors (ASSSCs) have received increasing attention. It's a great challenge to fabricate high-performance flexible solid-state supercapacitors with high areal and volumetric energy storage capability, superior electron and ion conductivity, robust mechanical flexibility, as well as long term stability. Herein, we report a facile method to fabricate flexible ASSSCs based on densely packed reduced graphene oxide (rGO)/polypyrrole nanoparticle (PPy NP) hybrid papers with a sandwich framework, which consists of well-separated and continuously-aligned rGO sheets. The incorporation of PPy NPs not only provides pseudocapacitance but also facilitates the infiltration of gel electrolyte. The assembled ASSSCs possess maximum areal and volumetric specific capacitances of 477 mF/cm(2) and 94.9 F/cm(3) at 0.5 mA/cm(2). They also exhibit little capacitance deviation under different bending states, excellent cycling stability, small leakage current and low self-discharge characteristics. Additionally, the maximum areal and volumetric energy densities of 132.5 mu Wh/cm(2) and 26.4 mWh/cm(3) are achieved, which indicate that this hybrid paper is a promising candidate for high-performance flexible energy storage devices. (C) 2016 Elsevier B.V. All rights reserved.