Wall or partition for an enclosure resistant to at least one mechanical aggression, said wall or partition comprising: - a first substantially full steel sheet with a thickness of between 2 and 5 mm and of which the lateral edges are folded to form a basin with a bottom, said folded lateral edges being advantageously welded to one another; - a series of panels including at least fibres (advantageously at least partially cellulosic) and a binder, the aforementioned panels presenting a density of at least 600 kg/m 3 and a thickness between 3 and 15 mm, - at least a second steel sheet substantially full, with a thickness 2 and 5 mm, and - at least one layer of expanded metal in steel with an apparent thickness ranging between 2 and 20 mm, advantageously between 2 and 8 mm, the mesh having a short diagonal ranging between 10 to 40 mm, advantageously between 20 and 30 mm, and a long diagonal ranging between 15 and 80 mm, advantageously between 40 and 60 mm, but greater than the short diagonal, defined by straps with a width included between 2 and 10 mm, advantageously between 3 and 7 mm, the aforementioned layer presenting an open passage area equal to 30 to 80% of the total area formed by the straps and the open passage area, in which the layer of expanded metal is located between a first fibre panel (advantageously at least partially cellulosic) and a second fibre panel (advantageously at least partially cellulosic) to form an entity including the expanded metal, and in which the aforementioned entity is located in the aforementioned basin of the first sheet between the aforementioned bottom and the aforementioned second steel sheet also located in the aforementioned basin of the first sheet. - a first substantially full steel sheet with a thickness of between 2 and 5 mm and of which the lateral edges are folded to form a basin with a bottom, said folded lateral edges being advantageously welded to one another; - a series of panels including at least fibres (advantageously at least partially cellulosic) and a binder, the aforementioned panels presenting a density of at least 600 kg/m 3 and a thickness between 3 and 15 mm, - at least a second steel sheet substantially full, with a thickness 2 and 5 mm, and - at least one layer of expanded metal in steel with an apparent thickness ranging between 2 and 20 mm, advantageously between 2 and 8 mm, the mesh having a short diagonal ranging between 10 to 40 mm, advantageously between 20 and 30 mm, and a long diagonal ranging between 15 and 80 mm, advantageously between 40 and 60 mm, but greater than the short diagonal, defined by straps with a width included between 2 and 10 mm, advantageously between 3 and 7 mm, the aforementioned layer presenting an open passage area equal to 30 to 80% of the total area formed by the straps and the open passage area, in which the layer of expanded metal is located between a first fibre panel (advantageously at least partially cellulosic) and a second fibre panel (advantageously at least partially cellulosic) to form an entity including the expanded metal, and in which the aforementioned entity is located in the aforementioned basin of the first sheet between the aforementioned bottom and the aforementioned second steel sheet also located in the aforementioned basin of the first sheet.