Preforms are loaded into a hopper, oriented (neck upwards), and fed into the heating section. Some machines have automatic unscramblers to line them up properly. The preforms are heated by infrared lamps (heating zones), rotating or travelling through heater ovens so that the body of the preform softens. The neck is often kept cooler (via neck cooling) because it must retain shape for fitting caps. Heat must be uniform to get consistent wall thickness in final bottles.
Once heated to the right temperature, the preform is transferred into a mould. A stretch rod pushes into the preform to elongate it vertically (stretch), then high-pressure air blows it radially into the shape of the mold (blow).