Included within this pack are twelve repellent mats that sit snugly inside your Thermacell Backpacker Mosquito Repeller. Each mat lasts 4 hours in total (48 hours as a total pack) and is simple and easy to replace for further protection. These mats are specifically designed for the Thermacell Backpacker Repeller system. 12 mats 4 hours of protection each Simple and easy to replace 15-foot zone of protection Mat-only refill for use in the Thermacell Backpacker Mosquito Repeller No spray and no mess. Scent-free and DEET-free. Active ingredient is Allethrin, a synthetic version of a naturally occurring repellent found in chrysanthemum flowers