STRONG, ELASTIC HYDROGELS ARE MADE BY COPOLYMERIZING ACRYLONTRILE OR METHACRYLONITRILE OR MIXTURES THEREOF WITH CO-MONOMERS HAVING HYDROPHILIC SIDE-GROUPS, SUCH AS ACRYLAMIDE, METHACRYLAMIDE, ACRYLIC ACID, METHACRYLIC ACID AND VINYL PYRROLIDONE OR WITH MIXTURES OF SUCH CO-MONOMERS. THE COPOLYMERIZATION IS CARRIED OUT IN PRESECE OF FREE RADICALS AND IN AN INORGANIC SOLVENT WHICH DOES NOT UNDERGO ANY SUBSTANTIAL CHAIN TRANSFER SUCH AS CONCENTERED AQUEOUS ZINC CHLORIDE SOLUTION OR NITRIC ACID.