The process starts with a resin that feeds into an extruding machine. As the resin is fed through a heated screw, it is forced to mix and melt to a liquid state. The screw forces the melted resin through a die forcing it into a tube. Blowing air through the center of the die ring expands the tube, sometimes called a bubble (much like blowing up a balloon). The amount of air and speed in which the tube travels up a tower determines the size and thickness of the plastic. The bubble travels up a tower to cool the melted plastic. Once cooled, the bubble is flattened and travels down the tower through a set of rollers. When the plastic reaches the bottom, it is wound on a large roll.