Presently, most passenger-side air bag doors are formed in an air bag cover that is separate from the instrument panel because the latter is made of a commercially available thermoplastic material particularly suited to meeting the requirements of its application but is not well suited to meeting the requirements of an air bag door that is defined by a tear seam formed in the instrument panel. For example, the plastics materials used to make a self-supporting instrument panel must have a certain degree of stiffness and high heat resistance to meet the requirements of its application but the materials that are currently available for such an instrument panel do not retain ductility and become embrittled at very low or cold temperatures which is unsuitable for air bag deployment where the air bag door is formed integral with and defined by a tear seam formed in the instrument panel. Styrene-maleic anhydride, polypropylene, polycarbonate and polyphenylene oxide are examples of thermoplastic materials that are suitable for the instrument panel but do not have the required ductility or flexibility for such an air bag door at very low temperatures. As a result, the air bag cover or door on the passenger side is normally made separate from the instrument panel and of a different commercially available thermoplastic material such as polyurethane elastomer, polyester elastomer, and polyolefin elastomer which are suitable for such application but are not suitable for the requirements of the instrument panel.
Costs can be reduced, quality can be improved and styling can be enhanced by molding the instrument panel and the air bag cover including an integral air bag deployment door in one piece at the same time out of the same commercially available material provided, however, that the normal material requirements for the instrument panel are not sacrificed and the safe assured operability of the integral air bag deployment door is retained at reasonable cost, even though the plastics material may not be well suited thereto.