The use of flat membrane humidifiers increases efficiency and extends the lifetime of fuel cells by humidifying the inlet airstream. The conditions under which the membranes mainly operate are determined by humidity, temperature, and pressure. The flat membrane humidifier uses the cathode-outflow of the flue cell to humidify the inlet airstream. Commonly available PFSA sandwich membranes are not necessarily designed to suit these operational conditions. Delamination of PFSA and the reinforcement layers may occur due to weak connection between the different layers. A delamination may lead to leakage, which could result in a bypass and pressure loss of the in- and outflow of the fuel cell. As a consequence, delamination of the PFSA membrane may cause failures of the flat membrane humidifier operation. To avoid delamination under such thermal and humidified conditions, it is necessary to strengthen the membrane during preparatory production steps against delamination. This paper examines different methods to strengthen the sandwich membrane against delamination due to water intake. It compares the effect of different sealing processes, focusing on increasing resistance against delamination. The investigated methods can also find application in PFSA membranes used under similar conditions, such as fuel cells. The technology selection process is focused on technologies enabling the flat membrane humidifier mass production for the automotive supplier MAHLE.