Plastic bottles are not as sturdy as glass bottles, which have large implications in the beverage industry.
One reason is glass bottles can be hot filled and sealed so that when they cool a vacuum is formed and the concentration of oxygen in the headspace is very low. If you were to attempt a similar process using plastic bottles, the bottle will “panel” as the negative pressure on the inside of the bottle cannot hold up to the outside air pressure. Therefore, another method is needed to control the amount of oxygen in the headspace above the beverage in a plastic bottle.
One technology is a nitrogen drip. After a bottle is filled with cool (not hot) liquid it passes under the drip which deposits a small amount of liquid nitrogen in the bottle. When the nitrogen hits the liquid inside it evaporates - expanding and pushing the air out of the bottle so that all that is left is nitrogen gas. The bottles are then sealed, and the inside oxygen concentration is minimized without the risk of paneling. The result is a bottle that feels firm to the touch. Once you open the bottle, the bottle goes back to its original feel.