Ultra-High Bypass (UHB) or "propfan" jet engines received attention in the late 1980s as an economical and greener alternative to current GTF and ATF jet technologies. Development was partially prevented by concerns about cabin noise and R&D costs as well as by industry fears that the external propellers would being seen by some as a step backwards. Evidently, General Electric and NASA are reinvesting in the technology.

The design is ultimately a hybrid between a Turbofan and Turboprop, which was aptly named a Propfan or Unducted Fan. The process begins by using a turbofan engine with the fans relocated to the outside of the engine housing. As the exhaust from the turbofan engine is forced out, they pass over a turbine which is connected to a prop on the exterior, while the other prop is driven by the turbofan.