With polymer-metal hybrids becoming more commonly used as structural components it was investigated how they perform in complex environments with combined thermal, media, and mechanical loads. Special attention was put on media tightness under said loads. This paper sums up the activities of the polymer technology research group of the University of Kassel on hybrids produced by overmolding metal inserts. Investigations concerning joint strength and influence of (cyclic) temperature loads and chemical corrosion on media tightness of the joint were undertaken with different polymer-metal hybrid specimen geometries (simple and complex). In order to enhance adhesion and joint strength, different bonding agents and adhesives were used in the experiments. It could be shown that all joints of polymer-metal hybrids lost their tightness after being exposed to temperature ranges from 30 to +150°C due to their highly different thermal expansion behavior. An elastomeric intermediate layer of certain minimum thickness in order to compensate the relative movement of plastic and metal and thus maintain integrity of the joint regardless of temperatures is proposed.