Original Thermacell Mosquito Repellent Refills effectively repel mosquitoes by creating a scent-free 15 ft. zone of protection when used in fuel-powered Thermacell Repellers. Includes 48 hours of mosquito protection refills. Each repellent mat lasts up to 4 hours, and each fuel cartridge lasts up to 12 hours. Package contains 12 repellent mats and 4 fuel cartridges. Active ingredient is Allethrin, a synthetic version of a naturally occurring repellent found in chrysanthemum flowers.