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 holsters pockets provide storage for extra repellent mats and butane cartridges. EPA-evaluated for safety and effectiveness. One butane cartridge and three repellent mats included.