Metallic spacers are preferred for large-diameter, heavy-walled pipes or where high temperature resistance is required, as they offer superior structural support. Conversely, Non-metallic (HDPE or Polypropylene) spacers are ideal for cathodic protection scenarios because they act as electrical insulators, preventing the flow of current between the carrier pipe and the casing. For trenchless installations (HDD), choose spacers with low-friction runners to minimize installation torque and prevent damage to the pipe coating.