Several decades of application of polymeric insulators to overhead lines worldwide has allowed the opportunity to accurately assess service performance as well as test experience for this technology. Before installation, insulator quality is always verified through design as well as type testing. Moreover, manufacturers are responsible to perform required sample and routine tests as well. Still, in many cases purchasers require additional acceptance tests and independent laboratories have for years been offering a range of design, type and special tests conducted on polymeric insulators. Such laboratory test experience has demonstrated that polymeric insulators generally fail during interface testing and emphasis is therefore being devoted to interfacial issues that are not being well addressed by the current standards. For example, although IEC 62217 specifies tests on interfaces to verify quality, service, as well as laboratory test experience, has shown that composite insulators with poor adhesion of housing to core rod sometimes still pass. As such, the standard is now in the process of being revised by IEC TC 36/MT 19. The goal is to specify stricter criteria to ensure improved capability to detect insulators with defective interfaces during testing. This presentation summarizes long-term service experience with polymeric insulators on the transmission grid in the Czech Republic and discusses key aspects of what has been learned from design and type testing them over more than 25 years.