Abstract: A terpolymer material for the formation of soft contact lenses includes a major amount of hydroxy alkyl acrylate or methacrylate, between 0.01 and 0.25% of a diester cross-linking agent containing acrylic or methacrylic groups and having no free hydrophilic groups, and between about 0.5 and 10% of a free acid (typically acrylic or methacrylic acid) having an unsaturated double bond. The material is polymerized in the non-aqueous state to form a rigid terpolymer having physical characteristics established by the diester concentration. The non-hydrated terpolymer can be formed into a contact lens using conventional lens grinding techniques. Upon subsequent hydration, the water concentration of the terpolymer is determined by the free acid concentration in the starting composition.