Barrier films deposited on flexible substrates are indispensable for a lot of applications. These are, for example, flexible displays based on LCD or OLED devices, flexible solar modules, materials for thermal insulation (e.g., vacuum insulated panels) or food packaging. The abovementioned applications already reveal very different requirements of barrier properties. Barrier films for food packaging for example can be produced with a single evaporated film, whereas the encapsulation of LCDs or OLED devices on flexible substrates is more sophisticated. In general, the approach of a complex multilayer system is used to fulfil the requirements for these ultrabarrier applications. In addition to their barrier properties, these multilayer systems also have to exhibit high transparency for many applications. In this case, a layer system can be used, that is based on sputtered Al2O3 layers, which are separated by different types of intermediate smoothing layers. This paper describes the concept and development of the Fraunhofer PolO alliance (www.polo.fhg.de) with regard to ultrabarriers for different applications. The barrier improvement of sputtered Al2O3 films deposited in a roll to roll process is analyzed. Further, the lacquering of inorganic organic hybrid polymers (Ormocers (R)) is described and synergetic effects from the use of the hybrid polymers in combination with sputtered Al2O3 films are discussed. Finally the assembly of an all flexible OLED test device is described, showing the suitability of complex multilayer systems for ultrabarrier applications. (c) 2005 Elsevier B.V. All rights reserved.