CO2 is a nonflammable, colorless, odorless gas. Although not truly an inert, carbon dioxide is nonreactive with many materials and is often used for inerting purposes. It is also used as a shielding gas in the arc welding process due to its high heat conductivity and its ability to oxidize ferrous metals. Mixtures of carbon dioxide are often recommended to increase penetration of the weld. It is also the source of bubbles in soft drinks and other carbonated beverages. It is used in certain types of fire extinguishers that rely on its inert properties, density, and low temperature when released from high-pressure storage. In addition to its “inert” properties, carbon dioxide, as dry ice, is used to freeze a variety of foods.