The invention relates to a method of improving the cooling of a blown-gas cooling chamber or of a blown-air cooling section in a line for heat treating steel and/or aluminum, and/or of improving the quality of products for treatment by reducing the vibration generated by the cooling, in which jets of gas or air are projected against each of the faces of the strip traveling through said section or chamber. In accordance with the invention, the jets (58) of gas or air are emitted from blow tubes (52) fitted to tubular nozzles (51) arranged at a distance transversely on either side of the travel direction (100) of the strip (53), said jets being directed towards the corresponding face of the strip while being inclined simultaneously essentially towards the edges of said strip in a plane perpendicular to the panel of the strip and to the travel direction (100) of said strip, and towards the upstream or downstream end of the strip in a plane perpendicular to the plane of the strip and parallel to the travel direction (100) of said strip.