Facility for treating the surface of a moving substrate, comprising - a support (1; 101; 201) for the substrate, - a pressing roll (2; 102; 202) able to press the substrate against said support - a treatment unit positioned downstream of the pressing roll, with reference to the direction of travel of the substrate, said unit comprising -- injection means (37; 137, 137', 137"; 237, 237') for injecting a treatment gas towards said support; -- means (8; 108, 108', 108"; 208, 208') for transforming the surface of the moving substrate; characterized in that this facility further comprises - a containment cover (4; 104; 204) open in the direction of the support, said containment cover (4; 104; 204) being distinct from said treatment unit, this cover and this support defining an inner volume in which said treatment unit is received, this cover comprising a front wall called the upstream wall (42; 142; 242), facing towards said pressing roll, the end edge (42'; 142'; 242') of said upstream front wall (42; 142; 242) being positioned in the vicinity of said pressing roll (2; 102; 202); and - means (5; 37B; 137B; 237') for recirculating some of the treatment gas upstream of said injection means, so as to define a recirculation volume for the treatment gas, defined by the end edge of said upstream front wall, the pressing roll, the support and the upstream end of the treatment unit, - the smallest distance between the end edge (42'; 142'; 242') of said upstream front wall (42; 142; 242) and the pressing roll (2; 102; 202) being less than 15 millimeters, - the smallest distance between said upstream front wall (42; 142; 242) and the treatment unit being less than 20 millimeters, and - the smallest distance between the pressing roll and the treatment unit being less than 10 millimeters. - a support (1; 101; 201) for the substrate, - a pressing roll (2; 102; 202) able to press the substrate against said support - a treatment unit positioned downstream of the pressing roll, with reference to the direction of travel of the substrate, said unit comprising -- injection means (37; 137, 137', 137"; 237, 237') for injecting a treatment gas towards said support; -- means (8; 108, 108', 108"; 208, 208') for transforming the surface of the moving substrate; characterized in that this facility further comprises -- injection means (37; 137, 137', 137"; 237, 237') for injecting a treatment gas towards said support; -- means (8; 108, 108', 108"; 208, 208') for transforming the surface of the moving substrate; - a containment cover (4; 104; 204) open in the direction of the support, said containment cover (4; 104; 204) being distinct from said treatment unit, this cover and this support defining an inner volume in which said treatment unit is received, this cover comprising a front wall called the upstream wall (42; 142; 242), facing towards said pressing roll, the end edge (42'; 142'; 242') of said upstream front wall (42; 142; 242) being positioned in the vicinity of said pressing roll (2; 102; 202); and - means (5; 37B; 137B; 237') for recirculating some of the treatment gas upstream of said injection means, - the smallest distance between the end edge (42'; 142'; 242') of said upstream front wall (42; 142; 242) and the pressing roll (2; 102; 202) being less than 15 millimeters, - the smallest distance between said upstream front wall (42; 142; 242) and the treatment unit being less than 20 millimeters, and - the smallest distance between the pressing roll and the treatment unit being less than 10 millimeters.