Research and development of transparent insulation systems (TI-systems) has been ongoing for 20 years with transparent insulation materials (TIMs) used to replace standard opaque insulation materials. TIM not only performs similar functions to opaque insulation, reducing heat losses and controlling indoor temperatures, but allows solar transmittance of more than 50%. With a thickness of less than 20 cm, it can provide a financial return to building occupants when applied to building facades, maximising occupiable and sellable spaces in urban areas, without compromising thermal comfort within buildings. In this review of TI-systems for building applications, drawbacks to previous applications, cost trends, and analysis of the limitation in information from previous studies are discussed. A major drawback in the development of TI-systems identified is the lack of cost information; the payback periods for TI-systems used in previous renovation projects are virtually unknown. Simple payback period calculations were undertaken based on information available from a demonstration project documented by the Solar Heating and Cooling (SHC) Programme of the International Energy Agency (IEA) Task 20 "Solar Energy in Building Renovation". The calculations indicated an encouraging 5-8-year payback period for this particular case study. It was concluded that the simple payback period calculation may be used for feasibility studies to indicate the time required to recoup investment when installing TI-systems and to provide initial guidance for building designers when evaluating the potential application of TI-systents in their buildings. (c) 2007 Elsevier Ltd. All rights reserved.