Classification is determined by the primary material of the insulating body, not its appearance. A composite insulator with a fiberglass-reinforced polymer (FRP) rod and silicone rubber housing is classified under the 'materials other than glass or ceramics' heading regardless of its shape or function. Importers should ensure that technical datasheets clearly identify the housing and core materials to support correct classification.

Silicone rubber housings are preferred in heavily polluted or coastal environments because they maintain hydrophobicity over time, reducing leakage current. However, UV degradation, tracking, and erosion are long-term concerns. IEC 62217 and IEEE 1523 provide guidance on aging evaluation. Buyers sourcing from new suppliers often require accelerated aging test data and field-service references before approving a product for utility-scale deployment.