One package containing 12 individually wrapped genuine Butterfly brand 500CP (candle power) mantles. Note that Butterfly no longer manufacturers 350CP mantles and recommends the 500CP mantles for the 828 lantern.
Mantles are Slightly Radioactive
Mantles are soaked in a solution of chemicals that leaves them slightly radioactive. They are frequently used in high school science labs when teaching about radiation because they will cause a sensitive Geiger counter to react. The radioactive elements react with the heated gas to create additional light, making the Butterfly lantern one of the brightest lanterns available.
The radiation is extremely small and has a range of only about one inch. New mantles can be handled safely, but you should not carry a package of a dozen mantles in your chest pocket for long periods of time. Avoid injesting or inhaling the dust from a burned mantle.