ThermaCELL repels up to 98% of mosquitoes and also provides an odorless zone of protection against black flies, no-see-ums, and other biting insects. Cordless and compact, the system uses a single butane cartridge to heat an insect repellent mat that releases allethrin into the air. Undetectable to humans, allethrin is a synthetic copy of a natural repellent found in pyrethrum flowers. Each repellent mat lasts for up to four hours and provides protection for up to a 225 square foot area. For hands-free carrying of the ThermaCELL, attach the optional holster (sold separately) to your belt, backpack, or other object. The holster&&';;s pockets provide storage for extra repellent mats and butane cartridges. EPA-evaluated for safety and effectiveness. One butane cartridge and three repellent mats included.