Alvars are made by replacing part or all of the acetate groups in Gelva with acetaldehyde. Their viscosity varies with the degree of polymerization and their properties vary according to the extent of replacement of the acetate groups. The Alvar types do not cold flow when molded, are tougher, harder, and have better adhesion but are less resistant to weathering than the Gelva types. Other properties are about the same as those of the Gelvas. Alvars having 70 to 80 percent acetate group replacement are used chiefly in spirit type varnishes, lacquers, and enamels that must stand exposure to weather. Another Alvar type is used in injection and press molding. The high binding power of the resin permits the use of large percentages of filler without loss of desirable properties. Such moldings may be machined and polished, and take inserts, such as the wood core in shoe heels. Flexible phonograph and transcription records made from the Alvars have gained wide approval. An 85 percent (acetate replacement) type has better impact strength and is used in toilet articles. Sheets, rods, and tubes of this resin may be machined in much the same way as nitrocellulose plastic and used where noninflammability is an asset. Formvars are made by replacing part or all of the acetate groups in Gelva with formaldehyde. These resins are colorless, odorless, tasteless, and thermoplastic. They have higher softening points and greater tensile and impact strength than the Alvars. They are resistant to alcohols, coal-tar solvents, fats, oils, or water. Moisture transmission rate through a film of this resin is about one-tenth that through regenerated cellulose and one-fourth that through cellulose acetate. The grades of the Formvars available are designated by the extent of replacement of the acetate group. The 75-percent replacement type has excellent mechanical strength and flexibility and is unaffected by sunlight. Formvars of 95 percent acetate displacement have a tensile strength as high as 10,000 pounds per square inch and offer possibilities in the manufacture of artificial silk and photographic film. The vinyl resins have made possible a new type of safety glass superior to any heretofore marketed. By condensing butylaldehyde with vinyl acetate, a polymer is obtained which is used as the inner layer between two sheets of glass. Heat and pressure secure complete adhesion and yield a sheet with greater resistance to breakage at low temperatures than the types now in general use.