Canister for filtering fuel vapours coming from a motor-vehicle fuel tank, wherein said canister comprises a hollow body defining at least one chamber containing adsorbing material for adsorbing fuel vapours, said material being in the form of particles or granules, and said canister having a first opening for communication to a vent conduit of the tank, a second opening communicating with the atmosphere, and a third opening for communication to a conduit connected to the intake manifold of the internal combustion engine of the motor-vehicle, in such a way that when the internal combustion engine is inactive, any fuel vapours generated within the tank are adsorbed by said adsorbing material, whereas when the internal combustion engine is in operation, an air flow taken from the atmosphere through said second opening is drawn into the chamber of the canister and conveyed through the adsorbing material and through said third opening towards said conduit connected to the intake manifold of the internal combustion engine, thereby obtaining a scavenging of the adsorbing material with a removal and conveyance into the engine of the fuel particles previously adsorbed by the adsorbing material, wherein within the chamber of the canister there are arranged one or more sheets (F1, F2, F3, F4, F5, F6), of a material substantially impervious to air, which are freely floatably supported within the particles or granules of adsorbed material, in such a way as to define a tortuous path of communication between said second opening communicating to the atmosphere and said third opening communicating to the intake manifold of the internal combustion engine, wherein said at least one chamber (180;181,182) has two opposite end walls (14, 16) and extends along a longitudinal direction between said end walls, and said sheets (F1-F5) are arranged along planes substantially orthogonal to said longitudinal direction, said canister being characterized in that said sheets impervious to air (F1-F6) are flexible sheets made of felt, paper or cardboard, synthetic material or metal material, floatably supported within the particles or granules of adsorbed material, including: at least one first flexible sheet arranged substantially at the centre of said chamber, along a plane orthogonal to said longitudinal direction, and occupies an area which is smaller than the area of a cross-section of said chamber along said orthogonal plane, so as to leave a peripheral free space around said flexible sheet for passage of air, and at least a second flexible sheet arranged substantially along a plane orthogonal to said longitudinal direction, which is longitudinally spaced from the plane of said first sheet and occupies substantially the entire area of a cross-section of said chamber along said orthogonal plane, said second sheet having a central aperture defining a passage for the air, in such a way that the airflow through the canister during the scavenging stage is compelled to pass through said peripheral free space and through said central aperture of the first and second flexible sheets, thus advancing through the chamber in such a way as to reach all the areas of the chamber. at least one first flexible sheet arranged substantially at the centre of said chamber, along a plane orthogonal to said longitudinal direction, and occupies an area which is smaller than the area of a cross-section of said chamber along said orthogonal plane, so as to leave a peripheral free space around said flexible sheet for passage of air, and at least a second flexible sheet arranged substantially along a plane orthogonal to said longitudinal direction, which is longitudinally spaced from the plane of said first sheet and occupies substantially the entire area of a cross-section of said chamber along said orthogonal plane, said second sheet having a central aperture defining a passage for the air, in such a way that the airflow through the canister during the scavenging stage is compelled to pass through said peripheral free space and through said central aperture of the first and second flexible sheets, thus advancing through the chamber in such a way as to reach all the areas of the chamber.