There is no method that can determine the exact average age of paper insulation, but there are well-established indirect techniques to estimate its remaining life. The most common is furan analysis of the oil, which correlates furan concentration with the degree of polymerization (DP) of cellulose. DP gives a good indication of mechanical aging. Additional methods include trend analysis of moisture, acidity, CO/CO? ratio in DGA, and historical thermal loading. These together allow a reasonable estimate of insulation aging, but never a precise “age” in years.