Cream chargers, also known as whipped cream chargers, are small, metallic cylinders or cartridges filled with nitrous oxide (N2O). They are used with a whipped cream dispenser to whip cream.
The nitrous oxide in the charger is released into the dispenser, which is filled with heavy cream and sometimes sugar and other flavorings. The gas gets mixed with the cream under high pressure, and when the cream is released (like when you press the nozzle on a can of store-bought whipped cream), the pressure drop allows the gas to expand, whipping the cream.
It’s worth noting that while nitrous oxide is safe for this culinary use, it is also a potent greenhouse gas and it’s misuse can be dangerous. There has been a concern about the recreational misuse of these cream chargers, as inhaling nitrous oxide directly can lead to oxygen deprivation, which can be dangerous or even fatal.