According to the University of Kentucky College of Agriculture, Food and Environment, roach bombs are seldom effective at killing roaches, no matter the brand. In most cases, very little of the insecticide sprayed by roach bombs penetrates into the deep cracks and crevices where roaches hide.
Roach bombs, or insect foggers, spray a fine mist containing an insecticide straight up into the air, where it disperses and settles onto floors and other surfaces. Roaches and other household insects spend most of their time in wall voids and other hard-to-reach areas, where the residue does not settle. In addition, most foggers use pyrethrin, which is somewhat effective on flying insects but rarely fatal to cockroaches.