Silica gel is used in the breather of oil filled power transformers to dry the air that enters the conservator as oil volume changes with temperature. Moisture in air can be absorbed by the insulating oil and paper, degrading dielectric strength and accelerating aging. The breather forces incoming air to pass through silica gel crystals, which adsorb moisture. When saturated, the crystals change color, indicating the need for replacement or regeneration. Maintaining dry air in the conservator system is a simple but important part of transformer maintenance.