Cascade cycles may be separated by either being sealed in separated loops or in what is referred to as an "auto-cascade", where the gases are compressed as a mixture but separated as one refrigerant condenses into a liquid while the other continues as a gas through the rest of the cycle. Although an auto-cascade introduces several constraints on the design and operating conditions of the system that may reduce the efficiency, it is often used in small systems due to only requiring a single compressor or in cryogenic systems as it reduces the need for high-efficiency heat exchangers to prevent the compressors leaking heat into the cryogenic cycles. Both types can be used in the same system, generally with the separate cycles being the first stage(s) and the auto-cascade being the last stage.