Dry ice is solid carbon dioxide, CO2. It is made by compressing and cooling gaseous carbon dioxide (CO2) until it liquefies.
Expansion converts the liquid into the snow form of the solid state. The snow is then compressed by a hydraulic press into dry ice blocks, slices or pellets.
Solid Carbon Dioxide - CO2 is very cold: -78°C. It sublimes (turns from a solid) to an asphyxiant gas that is heavier than air. It is important to note that a little bit of dry ice will sublime to a large volume of gas.