Air-conditioning duct for conveying and/or distributing air, comprising - a peripheral wall, - an inlet for supplying air, - a regulating membrane made of air impermeable woven or non-woven fabric or of a foil, which membrane comprises a longitudinal portion arranged inside the air-conditioning duct and attached to the peripheral wall of the same along at least one line, said line dividing the peripheral wall of the duct into a first portion and a second portion, wherein the regulating membrane has a first end facing the inlet for supplying air and the membrane is at least in an area of its first end adapted for being selectively flipped to the first portion or the second portion of the peripheral wall of the duct, and - a flipping element for flipping the first end of the regulating membrane to the first portion or the second portion of the peripheral wall of the duct, the regulating membrane having its first end attached to the flipping element, characterized in that the regulating membrane has its second end, which faces away from the inlet of the duct, secured inside the air-conditioning duct in a manner which ensures that flipping of at least the area of the first end of the regulating membrane to the second portion of the peripheral wall of the duct causes the air flow to be prevented from passing through that portion of the air-conditioning duct which is situated downstream of the attached second end of the regulating membrane with respect to the direction of that airflow, wherein the flipping element has a shape corresponding to one half of the circumference of an oblique section through the air-conditioning duct, said section extending along a plane forming an angle between 30 and 80° with the longitudinal axis of the duct. - a peripheral wall, - an inlet for supplying air, - a regulating membrane made of air impermeable woven or non-woven fabric or of a foil, which membrane comprises a longitudinal portion arranged inside the air-conditioning duct and attached to the peripheral wall of the same along at least one line, said line dividing the peripheral wall of the duct into a first portion and a second portion, wherein the regulating membrane has a first end facing the inlet for supplying air and the membrane is at least in an area of its first end adapted for being selectively flipped to the first portion or the second portion of the peripheral wall of the duct, and - a flipping element for flipping the first end of the regulating membrane to the first portion or the second portion of the peripheral wall of the duct, the regulating membrane having its first end attached to the flipping element, characterized in that the regulating membrane has its second end, which faces away from the inlet of the duct, secured inside the air-conditioning duct in a manner which ensures that flipping of at least the area of the first end of the regulating membrane to the second portion of the peripheral wall of the duct causes the air flow to be prevented from passing through that portion of the air-conditioning duct which is situated downstream of the attached second end of the regulating membrane with respect to the direction of that airflow, wherein the flipping element has a shape corresponding to one half of the circumference of an oblique section through the air-conditioning duct, said section extending along a plane forming an angle between 30 and 80° with the longitudinal axis of the duct. characterized in that the regulating membrane has its second end, which faces away from the inlet of the duct, secured inside the air-conditioning duct in a manner which ensures that flipping of at least the area of the first end of the regulating membrane to the second portion of the peripheral wall of the duct causes the air flow to be prevented from passing through that portion of the air-conditioning duct which is situated downstream of the attached second end of the regulating membrane with respect to the direction of that airflow, wherein the flipping element has a shape corresponding to one half of the circumference of an oblique section through the air-conditioning duct, said section extending along a plane forming an angle between 30 and 80° with the longitudinal axis of the duct.