An important task of the BALANCE project is the demonstration of the reversible Solid Oxide Cell technology at system level. This requires a high number of unit cells, which have been prepared in DTU unique manufacturing facilities. They are being shipped to CEA, who will assemble them into 2.5 kW stacks that will be used in VTT and CEA’s system platforms. These units cells are a key element to obtain high system performance and are the sums of years of research and development in materials science. One of the challenge is to make these unit cells gas tight using a brittle ceramic membrane, which is thinner than a human hair.