A closure material for sealing glass containers comprising a metal foil and a thermally adhesive composition layer formed on one surface of the metal foil and comprising a carboxyl-modified saponified product of ethylene-vinyl acetate copolymer and up to 30 parts by weight of an inorganic compound per 100 parts by weight of the carboxyl-modified saponified product, the carboxyl-modified saponified product being prepared by graft-polymerizing a carboxylic acid group-containing unsaturated compound with a saponified product of ethylene-vinyl acetate copolymer containing 50 to 97 mole % of ethylene.