We demonstrate the effect of bundle structure, composed of multiwalled carbon nanotube (MWCNT) material in disordered MWCNT electrodes, on electric double-layer capacitor (EDLC) performance (i.e., their rate capability and specific capacitances). This is done by applying two types of MWCNTs with low (50-100) and high (2500-10,000) aspect ratios of their length to diameter. The use of these physically opposite values elucidates how the electronic pathways, pore distribution, and sidewall/edge balance of MWCNTs contribute to these electrodes' kinetic and capacitive performance for EDLC. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.3049907] All rights reserved.