The ThermaCELL(R) Mosquito Repellent Refill Unit Value Pack uses Allethrin to provide 48 hours of repellency and cover scent. Each cartridge lasts for 12 hours, while each mat lasts for four hours. These components may be used separately. The refills are safe for long-term storage and fit all ThermaCELL mosquito repellent models. FEATURES: Mosquito repellent Refills safe for long-term storage Each cartridge lasts up to 12 hours Each mat lasts up to 4 hours Cartridges and mats do not required simultaneous use Fit all ThermaCELL(R) mosquito repellent models If time between uses is more than a 1 week, store the mat in a dry, dark place Repellent: Allethrin Includes 12 insect repellent mats and 4 butane cartridges Pack contents provide 48 hrs. of repellency and cover scent Model: MR400-12