Abstract: An insulated vinyl window frame includes at least one passageway having insulation disposed therein. The insulation may be either foamed in place or rigid material which is formed to size and then inserted into the passageway during assembly of the frame. Preferably, the passageway walls include a plurality of ribs which position the rigid insulation a small interval from the walls defining and sealing off air spaces between the walls and the insulation thereby providing small, substantially non-circulating regions of air. Since the air has a heat resistance value greater than most other construction and insulating materials such as plastic, glass, rubber or metal, the window frame exhibits extraordinary insulating characteristics.