The hydrogels described here are copolymers of acrylamide and methacrylamide highly cross-linked with piperazine diacrylamide or 4, 7, 10-trioxa-1, 13-tridecanediamine diacrylamide by radical polymerisation in highly concentrated aqueous and aqueous gelatin solutions. The hydrogels were characterised by their compressive strength, refractive indices, densities, ‘free’ water contents and degree of swelling. The hydrogels cross-linked with piperazine diacrylamide gave strong glassy hydrogels, which we have termed “hydroglasses”. Cross-linking with 4, 7, 10-trioxa-1, 13-tridecanediamine diacrylamide, which contains a long flexible spacer, did not result in a more elastic gel. Polymerisation in an aqueous gelatin solution improved the mechanical properties of the gel eno