Electric and electronic components have to be encapsulated, whenever protection against humidity, chemical agents, foreign particles and vibration as well as enhanced thermal conductivity is important. Nowadays mostly polyurethane potting resins are used for that kind of potting applications as the offer advantageous mechanical properties like a good tear resistance and flexibility. Further they are preferred for economic and health reasons. As the market offers a big variety of different products, this paper informs the user about selection criteria. In a first step it is explained, which values are shown on technical data sheets and how to read them. Measuring methods of the various process parameters and thermomechanic properties are explained. Further, this paper gives background about the different requirements of Underwriter Laboratories like UL94 flammability test, UL746 RTI test, HWI and HAI test. Most polyurethane resins allow variation of process parameters like curing and gelation time. This paper gives a definition of these parameters and explains how they can be adapted to an existing process.