Are double-walled insulated cups the hype?

These days it is common to see high quality drinkware with double wall vacuum insulation.

Sounds fancy! But what does this particular feature really mean, apart from being a buzzword? Does putting a layer of air between your drink and the outside world really keep your drink at the ideal temperature for longer?

Surprisingly, the history of the invention of double insulation dates back to a cryogenic researcher in 1892.

While we don't believe people were sipping their drinks from completely insulated cups at that time, Sir James Dewar did have something going on and was way ahead of his time with the development of his drinkware!

Description of the double-walled vacuum construction

In short, the body of a double-walled vacuum-sealed flask or glass is made of two layers of stainless steel or similar material.

The walls are kept at a distance from each other, so that there is a little open space between both the inner and outer walls.

This ensures that a vacuum is created: a space where no air molecules are floating around.

A true vacuum is the same as the one experienced when leaving the earth's atmosphere!

So how does it help you to keep your drinks at the optimum temperature?

Because a vacuum affects heat convection and conduction, double-walled vacuum insulated beverage containers can keep your drinks at the ideal temperature (hot or cold).

Without getting too involved in the science, heat can basically be thought of as the vibration of different molecules.

The laws of thermodynamics require thermal vibrations to shift over time from fast vibrating molecules to slower vibrating molecules or atoms.

Heat 'likes' to eventually reach equilibrium: a state where all surrounding atoms and molecules vibrate at approximately the same speed.

This is why heat is transferred from a hot object or liquid to a cold object or liquid (and not the other way around). Technically, there is no such thing as "cold". There is just not enough heat!

Having said that, heat can only be transferred from one molecule to another, provided they are very close together.

A hoover itself does not have any air molecules to facilitate the transfer of heat from the liquid inside the glass or water bottle to the outer walls.

The vacuum acts as a barrier, reflecting the heat from the hot liquid back into itself.

This also prevents any heat from escaping to the outer walls and eventually transferring to the surrounding air.

The heat 'likes' to eventually reach equilibrium: a state where all surrounding atoms and molecules vibrate at approximately the same speed.

Similarly, double-walled vacuum insulated hot water bottles and glasses prevent heat from the surrounding environment from exceeding the vacuum threshold and reaching your cold liquid, thus keeping your drink cool.