In the Book Hygiene and Restoration Department of the M. E. Saltykov-Shchedrin State Public Library in Leningrad a new method of paper restoration is used involving strongly diluted paper pulp containing polyvinyl alcohol fibers. The paper made of cotton fibers and polyvinyl alcohol was tested after exposure to different unfavorable conditions: heat, fluctuations of temperature and humidity, freezing, an atmosphere of SO₂, and light. It is determined that the stability of the studied paper is greater than the stability of the paper containing only cotton fibers. The calculation of the paper durability is carried out on the basis of kinetic theory of strength. Author's address: State Public Library, Leningrad, USSR.