Approved by the PRMA, ThermaCELL is ideal for outdoor activities. ThermaCELL uses a repellent called allethrin, a man made copy of a naturally occurring repellent found in a member of the chrysanthemum family-an effective alternative to DEET. How it works : The butane energy cartridge heats the repellent mat. The mat releases the repellent into the air, creating ThermaCELL's 15'x 15' mosquito-free-zone within 30 minutes. Undetectable to game. No smelly, sticky, lotions or sprays. Pocket sized and portable. Each appliance includes one butane cartridge and three mats for up to 12 hours of protection.