Open the package and expose the Warmer to air and it will immediately start to heat up! Each Heat Treat pouch contains iron, cellulose, vermiculite, activated carbon, salt and water. When the iron is exposed to oxygen, it starts to oxidize and produces heat. The salt acts as a catalyst and the carbon helps disperse the heat. The vermiculite is an insulator to retain the heat. Cellulose is a fill. The average temperature is 100 degrees F. Non-toxic, environmentally friendly, all natural ingredients, odorless and non-combustible. 2 warmers included.