ThermaCELL® Mosquito Repellent Refill includes 12 mats and 4 cartridges, for a total of 48 hours of repellency. To continue to repel mosquitoes repellent mats should be replaced after 4 hours of use. Butane cartridges last up to 12 hours each. Refills fit all ThermaCELL mosquito repellent models.