eli5: Why do spray paint cans get cold when we shake them?



Don’t know if it happens to other cans as well but why do spray paint cans feel cold when we touch after shaking them?

In: Chemistry

When you hold the can, the outside of the can gets warm because your hand is heating it up.

When you shake the can, the cold paint inside stirs around and when the colder paint contacts the inside of the can, it feels cold again. If you’re shaking it constantly, it’ll constantly feel a little cold until all the paint has warmed up.

Actually using the spray can can cause the inside to get a little colder as well, since the propellent (the stuff inside the can that isn’t paint) is expanding, which causes it to cool down. Shaking it brings this cold fluid to the edges of the can.

They don’t.

They get cold when you *spray the paint*, because you’re releasing pressure from the can. Releasing pressure is an endothermic reaction, meaning that the remaining contents of the container (and thus the container itself) get colder.


Basically, in physics the pressure and volume have to balance out against the temperature. If you lower the (P)ressure (in this case without changing (V)olume), then you have a lower (T)emperature on the other side to balance out. (N and R are constants if I remember right.) It’s how refrigeration works too. You pump the coolant around and change the pressure to make things hotter or colder. It’s the same reason canned air gets colder too

There are actually many factors that contribute this.

The main one however is that the paint within the can is pressurized to a point such that both gas and liquid of the paint exist. This is called saturation. When you shake the can, you are not only mixing these two, but you are increasing the pressure inside the can.

This however does not explain why the can still gets colder when you use the can which intuition would tell you should lower pressure inside the can.

The answer to that, is that the pressure does not actually change within the can. As you use the saturated material that is a gas, the material that used to be liquid begins to boil and becomes gaseous. This is why the can always releases the gas in a steady stream until it is near empty. The pressure stays the same.

However it takes a lot of energy to change the material from liquid to vapor. This is what causes the drop in temperature

Edit: fixed-

Minute Physics has an excellent video on this which I will link to below:


Put some rubbing alcohol in your hand. As it evaporates it will remove heat from your skin and feel cold. The alcohol is turning from a liquid to a gas and it needs energy to change state. The can feels cold because the liquid propellant and paint in the paint can is turning to gas. This is how air conditioning works in your house. The outside unit compresses the refrigerant into a liquid. When the liquid gets to the indoor unit it goes through an expansion valve and it becomes a gas, which removes the heat from the air, just like the paint can getting cold. Then the hot gas goes back to the outside unit where it is cooled down and compressed again into a liquid. Hope that helps.