These aluminum cartridges store the life-blood of the Mammut Airbag system: simple compressed air. The cartridges can be purchased with or without a charge, noting there are transport restrictions on a charged unit (no air travel). Either one can be refilled using a compressed air source such as a SCUBA or paintball tank. To recharge a unit, you'll need a tank, adapter, and a refill kit that consists of a disposable gasket and cover plate. The cartridges are designed to hold 3000 PSI and weigh 625g empty or 700g with a charge.