The adhesive or interlayer of compound glass comprises essentially a partial polyvinyl acetal resin containing acetal groups, free hydroxyl groups, and substantially no others derived from a polyvinyl ester, e.g. the acetate having an average molecular weight of 7,000-25,000 or more and acetalized from 33 to 94 per cent with a saturated aliphatic aldehyde having 2-6 carbon atoms, the particular aldehyde, and the extent of its combination in the resin being so correlated that the resin is insoluble in water, aliphatic and aromatic hydrocarbons, and substantially insoluble in ester plasticizers at ordinary temperatures, but is compatible with substantial proportions of ester plasticizers to yield homogeneous compositions of high extensibility and resiliency and high ultimate strength. The degrees of acetalization with the different aldehydes are quoted in the Specification and illustrated by a graph. The plasticizer may be dibutyl phthalate, di(b -butoxyethyl) phthalate, or triethylene glycol di (2-ethyl butyrate) and may be mixed with the resin with the aid of heat or a volatle solvent or non-solvent liquid such as water, acetone, ether, or benzene. The wet resin obtained from the reaction chamber may be mixed with the plasticizer at an elevated temperature. The plasticized resin is sheeted by extrusion, calendering, or evaporation of a solution, e.g. on one of the glass sheets.