A barrier structure intended for the storage and/or transport of fluids including at least one barrier layer (1) including an MXDT/XT copolyamide in which: MXDT is an amide unit present in a molar ratio of between 5 and 45%, preferably between 15 and 45%, and more preferably between 20 and 45%, where MXD represents m-xylylenediamine (MXD) and T represents terephthalic acid, XT is a majority amide unit present in a molar ratio of between 55 and 95%, preferably between 55 and 85%, and 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, said copolyamide having a melting point: 250° C.