Everyone surely has drunk carbonated soft drinks or mineral water at least once in their lifetime. And if you pay attention, you will see that most of the bottle bottoms are always designed to be bumpy, never flat as glass bottles.

Many will think that’s just a decorative touch added by the manufacturers for their products? However, this is actually a rule that most beverage companies, especially carbonated soft drinks, must follow.

As you clearly see, the bottom of this plastic bottle usually has 5 protrusions in the form of folds. Their purpose is to increase the strength of the entire water bottle. You can try the same with a piece of paper. It can easily fold. However, if you curl then fold it, it will be much more difficult. Thus we know that bending any material will enhance its strength and stiffness (or increasing the moment of inertia around the bending axis in physics).

plastic bottle bottom axis
These plastic bottles' design maximizes their durability

Most plastic or soda bottles are served chilled and added carbon dioxide. When the liquid cools down and has gas, its volume changes, which may lead to the container being overpressured. Therefore, manufacturers must design the bottles in a way that the corner or top of the bumpy bottom can expand. 

In addition, the protrusions on the bottom of the plastic bottles can also absorb shocks when you accidentally drop them on the ground. If you don’t believe it, take out a plastic bottle and trample them. Certainly, you can only deform the top while the bottom will largely remain intact.

plastic bottle bottom
The soft drink bottles have a smaller top to lower its center

Besides, if you may also notice that soft drink bottles tend to increase in size from the top to the bottom. This helps lower its focus, combined with the uneven bottom, improves the stability of the entire bottle. Even soda cans have a bottom that bends inward to for a similar purpose.

plastic bottle bottom can
The soft drink cans' bottoms also have an indent for the same purpose

So now you know why soda bottles have an uneven bottom! Read on for more interesting stories on GuruGamer's features tab.