in a device for manufacturing composite plastic mouldings , at least two different reaction mixtures are injected simultaneously through different sprues into the cavity of a mould . during the injection time of at least one of the reaction mixture , the cavity is subdivided into two or more mutually isolated regions . following the injection of one reaction mixture , the separation between the regions of the cavity is removed and the at least partially liquid reaction mixtures converge in the separation plane . this device makes possible to join at least two materials having different properties in a single operation . it is useful for manufacturing bumper bars , spoilers , coach - work , and internal linings of motor vehicles .