Elongated sheet for covering agricultural crops for generating a greenhouse climate in the covered area, with an elongated basic film made of plastic, wherein in the central area of the basic film a ventilation area extending in longitudinal sheet direction is provided with a plurality of ventilation openings, wherein a cover film of plastics material extending in the longitudinal sheet direction of the basic film is applied to the ventilation area forming free spaces for air exchange and is firmly welded to the basic film via a plurality of connection areas following one another in the longitudinal sheet direction, wherein the cover film is configured as a single layer, characterized in that the material and/or the quality of the cover film is selected in such a manner, that the cover film, in a first state, lies flat against and/or on the upper side of the basic film at least substantially in the region of the free spaces and, preferably by convection of the heated air in the covered area, in a second state at least partially lifts off relative to the upper side of the basic film forming free spaces, wherein the first state is maintained up to a transition temperature T 1 of the greenhouse climate and wherein the second state is obtained and/or realized from the transition temperature T 1 of the greenhouse climate, wherein the transition temperature T 1 is greater than 20 °C, preferably greater than 30 °C, more preferably between 30 to 50 °C and in particular at 38 °C +/- 5 °C, in that the cover film and the material of the cover film is configured to be more elastic and softer and less rigid than the basic film and the material of the basic film and in that the cover film comprises a lower grammage than the basic film. wherein in the central area of the basic film a ventilation area extending in longitudinal sheet direction is provided with a plurality of ventilation openings, wherein a cover film of plastics material extending in the longitudinal sheet direction of the basic film is applied to the ventilation area forming free spaces for air exchange and is firmly welded to the basic film via a plurality of connection areas following one another in the longitudinal sheet direction, wherein the cover film is configured as a single layer, characterized in that the material and/or the quality of the cover film is selected in such a manner, that the cover film, in a first state, lies flat against and/or on the upper side of the basic film at least substantially in the region of the free spaces and, preferably by convection of the heated air in the covered area, in a second state at least partially lifts off relative to the upper side of the basic film forming free spaces, wherein the first state is maintained up to a transition temperature T 1 of the greenhouse climate and wherein the second state is obtained and/or realized from the transition temperature T 1 of the greenhouse climate, wherein the transition temperature T 1 is greater than 20 °C, preferably greater than 30 °C, more preferably between 30 to 50 °C and in particular at 38 °C +/- 5 °C, in that the cover film and the material of the cover film is configured to be more elastic and softer and less rigid than the basic film and the material of the basic film and in that the cover film comprises a lower grammage than the basic film.