Why Do Plastic Bottles Cave in During Cold Weather?

The force of air pressure can make bottles collapse in cold weather.
••• Design Pics/Design Pics/Getty Images

Maybe you have seen this happen yourself: A plastic water bottle or milk jug is left outside in the cold and the sides of the bottle collapse or cave in. Why does this happen? The secret lies in how air pressure works.

Scientific Background

When air temperature increases, air pressure also increases. Conversely, when air temperature decreases, air pressure decreases. In science class, this is known as Charles's Law (and is the reason hot air balloons work).

Pressure in a Bottle

If a bottle is capped and then left in the cold, the air inside the bottle cools faster than the air outside the bottle. This means the air outside the bottle is exerting more pressure than the air inside the bottle, and the bottle collapses.


The plastic bottle only collapses if the bottle is capped. Otherwise, the air temperature and the pressure of the air inside the bottle and outside the bottle remain constant.

Try it Yourself

If you want to try this experiment yourself, place a capped bottle in your freezer for a few minutes. When you take it out of the freezer into the warm air, the bottle will collapse. You can also fill a bottle with hot water, cap it and then place it in a bowl of ice water.

Fixing the Bottle

Usually, the bottle will return to its normal state when you remove the lid. Removing the lid lets the air temperature and pressure inside and outside the bottle equalize.

Related Articles

Why Does Soda Explode in Freezers?
Why Do Pop Rocks Explode When Mixed With Soda?
How to Make a Hard Boiled Egg Go Into a Coke Bottle
Easy Home Experiments Using Gas Laws
How to Convert hPa to Altitude
How to Make CO2
What Do Calcium Chloride & Baking Soda Make?
How to Make a 3D Volcano for a High School Project
Why Do Balloons Inflate When on a Bottle of Hot Water?
Can You Define These Impossible Science Terms?
Hazards of Sodium Carbonate
Test Your Knowledge on Middle School Science
How to Mix Vinegar & Baking Soda in a Bottle Rocket
How to Remagnetize a Compass Needle
Science Fair Project: How to Get an Egg Into a Bottle
How to Keep an Egg Soaking in Vinegar for a Science...
Examples of Evaporation & Condensation
How to Find Molar Concentration
The Effect of Temperature on Bubble Solution
Jet Propulsion Science Projects