In order to evaluate the effectiveness in flame retardant and explosion suppression of the infill, a comparative study of the fast cook-off performances in terms of destructive consequences was carried out between the fuel tanks with spherical explosion suppression infill (or explosion suppression balls for short) and those without. Cook-off experiments were performed on tanks with diesel fuel (-10PD) and jet fuel (RP-5), respectively, simulating the situation of fuel tanks of vehicles or aircrafts being cooked off. The sizes of the fireballs, the surface temperatures, and the parameters of heat radiation were recorded respectively with a video camera, a high-speed camera, an infrared thermal imager, and a heat flux meter. Results show that jet fire or even explosion of vapor cloud would occur while fuel tanks being cooked off so that the primary destructive activities are the thermal effect of jet fireball. The fuel tanks with explosion suppression balls out-performed those without for -10PD as well as for RP-5 in terms of the postpones of the initial combustions for 48 s and 121 s, the reduction in maximal cross-sectional areas for 65.72% and 42.44%, the decrease in the surface temperatures for 26.13% and 12.66%, respectively, and apparent decrease in heat flux damage consequences.