the wire f are entirely prevented by means of air jets e3 discharged from nozzle slots 27 the air jets e 3 being directed in an opposite direction to the direction in which the leakage flows l 1 would flow the nozzle slots 27 are situated proximate to the wire f at its edges at a distance d therefrom which is substantially the same as the distance d that nozzle slot 23 is spaced from wire f the distance d is generally in the range of between about 10 to 20 mm and preferably about 15 mm so that there is no contact of the wire f with nozzles 27 in the embodiments of fig4 and 5 and as best seen in fig3 the narrowing gap n formed by the drying cylinder 10 and the wire f is closed at both edges of the wire f by means of wedge shaped portions 28 of side walls 26 wedge shaped portions 28 being shaped in accordance with the shape of the narrowing gap n alternatively wedge shaped plates can be attached to the blow box in fig3 the run of the web supporting wire f w is illustrated as being horizontal before the narrowing gap n for the sake of simplicity.