ThermaCELL Lantern Refill Pack: Thermacell works by heating a mat saturated with mosquito repellent. As the mat is heated the repellent is released into the surrounding area providing an area of protection (about 225 sq. feet)

The ThermaCELL Mosquito Repellent utilizes the active ingredient known as allethrin. It belongs to a class of materials called pyrethroids, which are synthetic analogs of pyrethrin, which is a naturally occurring insecticide found in certain types of chrysanthemum known as pyrethrum flowers. Mosquitoes really do not like this material. The allethrin is contained in the blue mats, and when they are heated it causes the allethrin to "volatilize", which is similar to evaporation. The volatilized allethrin forms a zone of protection around the unit The amount of active ingredient that is released is small - not enough to kill mosquitoes, but enough to repel them. There is 0.018 oz. of active ingredient on a mat.

Although the ThermaCELL Mosquito Repellent is most effective against mosquitoes, it has also been shown in field testing to be effective against black flies (Prosimulium hirtipes and Simulium venestrum), no-see-ums (Culicoides, also known as biting midges), and phlebotomine sand flies.
We do not have any data to support efficacy claims against the larger biting flies (horse flies, deer flies, greenheads)or common house flies. We also do not recommend it for bees, wasps, yellow jackets, or hornets. We do believe that it is effective in reducing or eliminating the annoyance of some non-biting insects such as gnats, but we do not have field test data to support this claim.

The ThermaCELL Mosquito Repellent is registered with the Federal EPA and with the EPA of each and every state. (Note: during the registration process the EPA evaluates insecticide products for safety and efficacy as well as environmental impact.)