A method of twin-sheet vacuum forming plastic articles having the steps of clamping two parallel sheets of thermoplastic synthetic resin in a vertical orientation to a clamping tray and blowing air between the parallel sheets thereby creating a hollow cavity between the two parallel sheets. The two parallel sheets are then heated to molding temperature between two vertically oriented heaters. The two parallel sheets are disposed between opposing mold cavities of a vertically oriented split mold wherein the mold cavities have a contour conforming the configuration of the desired article. A negative pressure is applied to suction holes provided in the mold cavities which draw the two parallel sheets against each opposing mold cavity. The split mold is then clamped together to form a pinch off around the perimeter of the hollow cavity thereby forming a molded hollow part still disposed within the clamping tray. Simultaneously, a blow pin inserted into the hollow cavity injects compressed air further presses the heated sheets against the mold cavities. The molded hollow part is allowed to cool to a set point and the vertically oriented split mold is opened. The clamping tray is withdrawn from the split mold and shuttled away from the mold cavities where the molded hollow part is cut away from the clamping tray, still in a vertical position.