A refrigerant for a cooling device includes a cooling circuit with at least one heat exchanger, the refrigerant undergoing a phase transition in the heat exchanger, the refrigerant being a refrigerant mixture composed of a mass fraction of carbon dioxide, a mass fraction of pentafluoroethane, and a mass fraction of at least one other component, wherein the mass fraction of carbon dioxide in the refrigerant mixture is 20 to 74 mass percent, the mass fraction of pentafluoroethane being 8 to 65 mass percent, the other component being fluoromethane.