Not all CO2 cartridges are the same, and for an item that can make the difference between continuing a ride and making a phone call for a bail out, you'll want a cartridge that has been certified for safety. Silca's Ultra-Premium CO2 Cartridges are so well-designed they are used in life vests and airbags. While 16-gram cartridges are only required to hold 14 grams of CO2, Silca ensures that its cartridges hold 15. 5 to 16 grams so that you'll get the maximum fill with each use. They are ISO, TUV, and RoHS certified and are also used in military and aviation life vests and avalanche bags. The Silca Ultra-Premium CO2 Cartridges come in a two-pack and are 16 grams each.