Polymeric transmission line insulators offer significant advantages over porcelain and glass insulators, especially for ultra HV transmission lines.

Their light weight allows tower designs and compacting that porcelain and glass insulators do not. Composite insulators can be used as phase spacers on compact lines to control galloping and to limit conductor motion due to through-faults. They have generated considerable interest among utilities, including quality control and testing requirements. Early evaluations indicated that their withstand performance was "equal to or better than that of a comparable length of porcelain insulator chain". More recent tests have generally verified these evaluations. Lack of intermediate electrodes, and small diameter, contribute to this improved performance.

The specific advantages of composite insulators, compared with ceramic insulators are:
Light weight-lower construction and transportation costs
Vandalism resistance - less gunshot damage
High strength to weight ratio-longer spans/new tower
Better contamination performance
Improved transmission line aesthetics

The reason for using composite insulators varies among utilities, but one of the most common reasons is connected with the low weight. The weight of a composite insulator is normally only about 10% of the equivalent porcelain or glass type. Composite insulators enable lighter tower designs or upgraded existing lines. Another important reason is associated with cost reduction, which would include lower cost for transport and construction, for narrower rights of way and for less maintenance.

Recently, composite insulators, especially those for application in transmission lines, have actually become cheaper than counterparts made of glass and porcelain. Many countries adopt composites to replace porcelains or glasses for advantages of composite insulators.