Abstract: The specification describes urethane foam automobile seats having variable firmness or density or varying in some other property from one portion of a seat to another by combining several hardenable precursor constituents in a predetermined ratio and discharging the resulting mixture through a single nozzle into a predetermined place in the mold and then changing the constituents and/or ratios of the constituents as the mixture discharges into other parts of the mold to produce the desired property in each part of the seat. The mixing of the various constituents is under the control of a computer programmed to deliver to each mold a series of shots of the polymer mixture, each constituent being supplied at the proper rate, and gradually and simultaneously changing the flow of each constituent at the beginning and end of each shot to maintain a consistent ratio within each shot yet allowing a change of ratios from one shot to the next.