干冰是二氧化碳的固体形式。在正常气压下，二氧化碳的凝固点是摄氏负78.5度，在保持物体维持冷冻或低温状态下非常有用。其无色、无味、不易燃、略带酸性。干冰的密度各不相同，但通常约为1.4至1.6 g/cm。干冰能够急速的冷冻物体和降低温度并且可以用隔离手套来做配置。现在干冰已经广泛的使用在许多层面，干冰在增温时是由固态直接升华为气态，直接转化为气体而省略转为液态的进程，因此其相变并不会产生液体，也因此称做“干冰”。要将二氧化碳变成液态，就必须将气压增强至51大气压才会出现液态二氧化碳。

Dry ice, sometimes referred to as "cardice" (chiefly by British chemists), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods where mechanical cooling is unavailable.