Flexible electronics can have a long lifetime only if they are electrically and mechanically robust. When the device fails mechanically through the formation of the cracks or deformation, the electrical conductivity is influenced. Materials used in flexible electronics can be tested to determine their electro‐mechanical behavior using tensile straining and bending methods. These methods are best employed with in‐situ observation techniques. Different testing approaches will be described for brittle and ductile films on polymer substrates which are used to determine the reliability of flexible devices.