A barrier structure for the storage and/or transport of fluids, including at least one barrier layer (1) including an MPMDT/XT copolyamide in which: MPMDT is a unit with an amide motif having a molar ratio of between 5 and 50%, particularly between 5 and 45%, preferably between 15 and 45%, more preferably between 20 and 45%, where MPMD is 2-methyl pentamethylene diamine (MPMD) and T is terephthalic acid, XT being a unit with a majority amide motif having a molar ratio of between 50 and 95%, particularly between 55 and 95%, preferably between 55 and 85%, more preferably between 55 and 80%, where X is a C9 to C18, preferably C9, C10, C11 and C12, linear aliphatic diamine, and where T is terephthalic acid, the copolyamide having a melting point of 250° C.