Defined micro-leaks have been used as reference leaks in non-destructive testing for many years, for example in the adjustment, calibration and functional testing of helium leak detectors. Test leaks are also used in non-destructive testing training to teach the staff how to detect these “invisible” leaks. The traditional production of test specimens with defined leakage, however, is timecon suming and expensive. In addition, these specimens are susceptible to impacts and can break easily. A new approach for producing robust specimens with defined leakage is gas dynamic cold spraying, or cold spraying, where a very small opening is closed using an open-pore metal powder filling. This manufacturing process is particularly suitable for industrial purposes due to the good controllability of the production process. Unlike traditionally manufactured glass bodies, the specimens produced in this way are less susceptible to mechanical impacts. The present study is concerned with the metallographic examination of porous coatings to create defined leaks using cold spraying.