The Umarex NitroAir Cartridge is the first pre-filled, compressed nitrogen-loaded cartridge designed for use with N2-designated airguns. Not only is it the most innovative and revolutionary solution for high pressure airguns, but it is also the most convenient. Each cartridge in this 2 pack is compressed to 3,600 psi and has 32 grams of nitrogen (N2) in each one. These cartridges should only be used with airguns with the N2 symbol, indicating that the airgun is designed for use with these pre-filled, disposable nitrogen cartridges. These are NOT for use with CO2 powered airguns as those are designed for a significantly lower operating pressure. When cartridge replacement is necessary, use the air bleeding mechanism on the gun to empty all air before removal. When the cartridge is empty , you may recycle it at any place where steel is accepted.