Thermacell Backpacker Mosquito Repeller Mat & Gas RefillsThe Thermacell Mosquito and Midge Repeller Refills contain 12 insect repellent mats and 4 butane cartridges in a large pack or 3 insect repellent mats and 1 butane cartridge in a standard pack. Each high quality insect repellent mat will provide protection for up to 4 hours and each butane cartridge will last for up to 12 hours providing excellent protection from mosquito and midge bites. The mat and gas refills use a synthetic insect repellant that