Viszonylag új dolog lehet, jobbára szabadalmi leírásokban található. A levegő bevezető és kivezető nyílások között elhelyezett műanyag fólia, ami két, oldalt elhelyezett tengely között oda-vissza tekercselhető, így a rajta kiképzett áteresztő lyukak helyzete a kivezető nyílásokhoz képest állítható. Gyakran ugyanezt „film valve”-nek nevezik. Magyar nevet nem találtam.
„Air distribution apparatus for an automotive vehicle
United States Patent 5105730
Abstract:
An air distribution apparatus for an automotive vehicle, comprising a chamber for receiving air conditioned by at least one heat exchanger, the chamber includes an inlet opening and a plurality of discharge openings and mechanism downstream of the inlet opening for selecting at least one of the discharge openings. The mechanism for selecting comprises a pair of rollers, a flexible material disposed between the rollers and having at least one cutout area; and a mechanism for bidirectional driving of the rollers for positioning the flexible material such that the cutout area is either positioned for allowing air flow through at least one of the discharge openings or for preventing air flow through any of the discharge openings.”
http://www.freepatentsonline.com/5105730.html


„An alternative with potentially much better linearly, which is also more space effective, is a flexible film valve in which a roll of film is rolled back and forth, almost like a window shade, to block or unblock various openings to any degree desired. Existing film valve drives are expensive and complex, however. Two shafts are used with known designs, one to wind up an end of the belt and another to wind it off. Only one shaft may be powered, with the other shaft following along passively, with a return spring or other device used to maintain belt tension.”
www.patentstorm.us/patents/6074294-description.html

„Control with film damper
The step motor retracts the film damper with holes and adjusts the location of the holes to allow individual temperature and airflow control.”
http://youronlinemechanic.com/2007/11/19/automatic-aircondit...