Provides a classification system that serves as a guide for the selection and indexing of insulating materials intended to serve in the radiation environment of nuclear reactor facilities, reactor fuel-processing facilities, irradiation facilities, particle accelerators, and X-ray apparatus. The classification system provides a set of parameters defining the utility of the three types of polymeric materials (rigid plastics, flexible plastics, elastomers) for use in devices which are exposed to ionizing radiation. This part of IEC 60544 forms the basis for a quantitative statement of the suitability of such materials for radiation environments and therefore provides a guide for material specifications and for procurement agreements between suppliers and users. The purpose of the revision was to bring Part 4 in line with the revision of Part 1 (1994) and Part 2 (1991), in particular the fact that Part 3 has been incorporated in Part 2. This concerns mainly all the cross-references (which were wrong in the previous edition), and therefore the main changes were editorial.