The production cost of dry ice is 1 to 2 yuan, and the market price of dry ice is 3 to 6 yuan per catty. The composition of dry ice is carbon dioxide. When carbon dioxide changes from solid to gas, it absorbs a lot of heat, which makes the temperature of the surrounding air drop rapidly. When the air temperature drops, its solubility in water vapor becomes smaller, water vapor liquefies, and the released heat becomes small water droplets, which is fog.