A refrigerant for a cooling device including 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, a mass fraction of difluoromethane and a mass fraction of at least one other component, wherein the mass fraction of carbon dioxide in the refrigerant mixture is 28 to 51 mass percent, the mass fraction of pentafluoroethane being 14.5 to 32 mass percent, the mass fraction of difluoromethane being 14.5 to 38 mass percent, the other component being fluoromethane.