Dry ice

Dry ice is the solid form of carbon dioxide (CO2). In cryonics, it is used as a cooling agent for cryopatients, for example, when transporting them to long-term care providers. Dry ice sublimates at 194.7 K (−78.5 °C; −109.2 °F) at Earth atmospheric pressure. Dry ice is colder and more expensive than water ice, but warmer and cheaper than liquid nitrogen. Many cryonicists insist that dry ice is not cold enough for long-term cryopreservation.

Rhea Ettinger, the first patient of the Cryonics Institute, was placed in dry ice for about ten years until CI began using liquid nitrogen in 1987.