Windings consist of current-carrying conductors wound on the magnetic core and require appropriate insulation, support, and cooling to withstand operational and testing conditions. Power transformers primarily use copper and aluminum as conductive materials. While aluminum is lighter and often more cost-effective than copper, larger cross-sectional area aluminum conductors are required to match the performance of copper. Copper possesses higher mechanical strength and is used for all size ranges except the smallest, where aluminum conductors may be suitable. Transformers with aluminum windings are often larger than those with equivalent copper windings.