Polymer composites have frequently played a successful role in replacing metallic and ceramic materials. In many applications, polymeric materials have offered an alternative to glass (PMMA, PC) and aluminum in aeronautics, which have been replaced by polymer-matrix composites. Because of their lightness and ease of processing, polymers have long been used as electrical insulators, and the first work on extrinsically conductive polymers or polymers filled with electrically conductive particles was carried out in the 1950s (Hitory of polymeric composites). In composites with insulating matrices loaded with conductive particles, the transport of electric current is frequently confined to metallic or graphite particles. The conductive phase is often granular (carbon black, silver platelets, etc.) or fibrous (carbon fibers, aluminum fibers, etc.). Structural composites are structures using high-performance composite materials, often replacing metal structures.