Plant for the production by spun bonding or melt blowing of a web of a non-woven, comprising: - at least one melting station adapted to receive and melt a basic polymeric material; - an extrusion bar, in turn comprising a plurality of extrusion or drawing nozzles adapted to receive from the melting station the polymeric material in the molten state to produce a plurality of continuous filaments; - a conveyor belt adapted to advance along an advancing direction and to receive from the above said continuous filaments, produced by said extrusion nozzles, so as to form a web of a non-woven and continuously evacuate it from the plant; and - consolidation means for consolidating the web of non-woven formed on the conveyor belt; wherein said extrusion bar is variably inclinable with respect to the advancing direction of the conveyor belt; the plant being characterized by a special structure comprising a rotatable base platform adapted to rotate (f, f', f") about a respective axis of rotation with respect to a fixed part or structure of the same plant, and in that said melting station, adapted to receive and melt the basic polymeric material, and said extrusion bar, in turn comprising said plurality of extrusion or drawing nozzles to receive from the melting station the polymeric material in the molten state, are totally constructed and supported integrally by said rotatable base platform, so as to be rigidly connected to each other without the interposition of any rotary joint, whereby the plant allows to vary the width (L, L', L") of the non-woven web produced by the same plant, by rotating and adjusting said base platform around the respective axis of rotation, so as to vary the inclination (α, α', α") of said extrusion bar with respect to the advancing direction of the conveyor belt. - at least one melting station adapted to receive and melt a basic polymeric material; - an extrusion bar, in turn comprising a plurality of extrusion or drawing nozzles adapted to receive from the melting station the polymeric material in the molten state to produce a plurality of continuous filaments; - a conveyor belt adapted to advance along an advancing direction and to receive from the above said continuous filaments, produced by said extrusion nozzles, so as to form a web of a non-woven and continuously evacuate it from the plant; and - consolidation means for consolidating the web of non-woven formed on the conveyor belt; wherein said extrusion bar is variably inclinable with respect to the advancing direction of the conveyor belt; the plant being characterized by a special structure comprising a rotatable base platform adapted to rotate (f, f', f") about a respective axis of rotation with respect to a fixed part or structure of the same plant, and in that said melting station, adapted to receive and melt the basic polymeric material, and said extrusion bar, in turn comprising said plurality of extrusion or drawing nozzles to receive from the melting station the polymeric material in the molten state, are totally constructed and supported integrally by said rotatable base platform, so as to be rigidly connected to each other without the interposition of any rotary joint, whereby the plant allows to vary the width (L, L', L") of the non-woven web produced by the same plant, by rotating and adjusting said base platform around the respective axis of rotation, so as to vary the inclination (α, α', α") of said extrusion bar with respect to the advancing direction of the conveyor belt.