Blowing nozzle, in particular for stretching systems, comprising the following features - the blowing nozzle has a nozzle box, - the nozzle box has a lower face, two lateral walls which extend so as to be laterally spaced apart, and an upper face, whereby the nozzle box is formed having a chamber delimited by the lower face, the lateral walls and the upper face, - the nozzle box has an overall length, - the nozzle box has an inflow side at one end region thereof, with reference to its overall length, and a closure side on the side opposite the inflow side, - an exhaust opening arrangement is provided on the lower face such that a temperature transfer medium flowing in via the inflow side can flow into the nozzle box and flow out via the exhaust opening arrangement, characterised by the following further features - the nozzle box is divided in its longitudinal direction into at least two regions, specifically a first longitudinal region closer to the inflow side and a second longitudinal region that follows and/or is downstream of the first longitudinal region and/or further away from the inflow side, - the first longitudinal region is convergent or comprises at least one convergent portion in which the height between the lower face and the upper face is smaller than the height in the region of the inflow side as the distance from the inflow side increases, and - the second longitudinal region is divergent or comprises at least one divergent portion in which the height between the lower face and the upper face is greater than the height at the end of the first longitudinal region and/or at the beginning of the second longitudinal region as the distance from the inflow side increases. - the blowing nozzle has a nozzle box, - the nozzle box has a lower face, two lateral walls which extend so as to be laterally spaced apart, and an upper face, whereby the nozzle box is formed having a chamber delimited by the lower face, the lateral walls and the upper face, - the nozzle box has an overall length, - the nozzle box has an inflow side at one end region thereof, with reference to its overall length, and a closure side on the side opposite the inflow side, - an exhaust opening arrangement is provided on the lower face such that a temperature transfer medium flowing in via the inflow side can flow into the nozzle box and flow out via the exhaust opening arrangement, - the nozzle box is divided in its longitudinal direction into at least two regions, specifically a first longitudinal region closer to the inflow side and a second longitudinal region that follows and/or is downstream of the first longitudinal region and/or further away from the inflow side, - the first longitudinal region is convergent or comprises at least one convergent portion in which the height between the lower face and the upper face is smaller than the height in the region of the inflow side as the distance from the inflow side increases, and - the second longitudinal region is divergent or comprises at least one divergent portion in which the height between the lower face and the upper face is greater than the height at the end of the first longitudinal region and/or at the beginning of the second longitudinal region as the distance from the inflow side increases.