Describes a method for determining approximate lifetime of paper treated with polymeric additives. The process, developed at the State Public Library, Leningrad, involves placing paper samples under stress load and determining the folding endurance and stiffness. The author states that previously used methods of artificially aging paper by heat results in increased durability by the action of heat on the polymeric additives. Mathematical formulae are given for computing lifetime estimates from the folding strength. Based on experiments with the stress aging technique, surface treatment of 100% sulfate cellulose with a 3.5% solution of poly vinyl alcohol increased the service life from 80 years (untreated) to 900 year. Examples are given for 100% rag paper and newsprint.