Features: – fits to be installed to any plastic profile – no need to open the window to ventilate the room – no street noise and air drafts – Manual adjustment of air feed volume – Note! The installation of the window vent flapper does not require changes in profile. There is no need to drill a window!!! The principle of functioning: Fresh air from outside enters the channel between the frame and the sash in place of replacement of a fragment from typical seal to a special one. Then the air goes through a valve mounted on top of the flap and enters the room. Pls contact us for price and large quantities.