The systems of avalanche backpacks are based on an air cushion principle (Brazil Nut Effect), which inflates within seconds after release. In most airbag systems, this is done by using gas cartridges, which act as a activation unit. The different brands rely on different cartridge systems.
Basically, cartridges differ in the material (carbon / steel / aluminum), the content (air / nitrogen / CO2) and the weight.
On the market there are two types: cartridges that need to be replaced after use and refillable systems.