Why is synthetic transformer oil used instead of mineral oil?

Synthetic insulating fluids such as synthetic esters are used when higher fire safety, improved moisture tolerance, or better environmental performance is required. They generally have higher fire points than mineral oil, reducing fire risk in urban or indoor installations. Synthetic esters also can slow paper insulation aging by handling moisture differently, and may be preferred in sensitive areas due to biodegradability characteristics. Tradeoffs can include higher cost, different viscosity behavior, and materials compatibility checks.