NOVELTY - The gas-permeable cover comprises a rotary sidewall (2) of a biogas-container, where the cover comprises a surface element (6), which overstretches the inner room of the container. The surface element is formed by a fine-meshed textile web or textile. The mesh width of the surface element is less than 5 x 5 mm. Reinforcing elements (7) are firmly connected with the surface element. The reinforcing elements are arranged as girths, which are stitched with the surface element. Two fastening points are provided from each other on which the surface element is attached.    USE - Used as a gas-permeable cover.    ADVANTAGE - The gas-permeable cover can be simply, rapidly and economically manufactured.    DETAILED DESCRIPTION - The gas-permeable cover comprises a rotary sidewall (2) of a biogas-container, where the cover comprises a surface element (6), which overstretches the inner room of the container. The surface element is formed by a fine-meshed textile web or textile. The mesh width of the surface element is less than 5x 5 mm. Reinforcing elements (7) are firmly connected with the surface element. The reinforcing elements are arranged as girths, which are stitched with the surface element. Two fastening points are provided from each other on which the surface element is attached and the reinforcing element extends itself along the line between the reinforcing element of both fastening points, but stretch only over a part of the fastening points. The surface element comprises a lockable recess, where one of the surface elements are present on the material. The recess is provided with a lockable cover, which is attached by detachable closure elements on the surface element. The closure elements are arranged as hook closure. The cover is arranged in an area of its border in a color contrasting to the remaining surface element, which is arranged in the area adjacent to the cover in the color contrasting to the cover. The surface element comprises a middle recess and a central support (3) is connected at the edge of its recess with a holding ring (4). Openings are provided in the surface element, where the openings are larger than the mesh width of the surface element. The openings comprise edge reinforcement.    DESCRIPTION OF DRAWING(S) - The diagram shows a plan view of a cover.    Sidewall (2)    Support (3)    Holding ring (4)    Surface element (6)    Reinforcing elements. (7)