The preface of this article describes the qualities needed in plastics used in conservation and stresses the necessity to differentiate between the types, varieties and combinations of these plastics. The body of the article discusses the physical and chemical properties of several plastics from the point of view of their usefulness for conservation. Among the plastics discussed are: vinyl polychloride, vinyl polyalcohol and the polyvinylacetals. The vinyl polyacetate is examined at length, with its qualities reviewed in detail and its virtues distinguished from the characteristics of other polyacetals. The article recommends, however, prudence in the use of industrial polyalcohols because of the lack of literature on the results of studies and experiments abroad and the as yet insufficient results of experiments in French laboratories relative to the adaptability of this plastic to conservation. Finally, the article treats the properties and interior composition of polyacetals. It is suggested that this plastic could be used to conserve stone and other materials and as protection against ultra-violet rays if a glaze is added.