CO2 cartridges are small, pressurized containers filled with carbon dioxide gas. They are commonly used in various applications, such as inflating bicycle tires, powering air guns, and providing carbonation for beverages. The cartridges are typically made of metal and come in different sizes, with the most common being 12-gram cartridges. When the cartridge is punctured, the gas rapidly escapes, creating pressure that can be used for inflation or propulsion. CO2 cartridges are popular due to their convenience and portability, making them a practical choice for outdoor activities and recreational use. They are often found in sporting goods stores and online retailers.