Vacuum flask is an insulating container that can be used to store liquid and remain the liquid in the same temperature as long as possible by preventing heat transfer

Vacuum flask is an insulating container that can be used to store liquid and remain the liquid in the same temperature as long as possible by preventing heat transfer.
The two pictures below display the basic structure of a vacuum flask. It usually has a plastic screw-on stopper, a outer case, an inner chamber and the insulated support. The inner chamber contains two layers of glasses with silvered surfaces (inner layer & outer layer). There is a vacuum between the two layers. The design of vacuum flask is made by considering three ways that heat can be transferred, which are conduction, convection and radiation.
Firstly, the vacuum flask prevents the conduction and convection by the design of vacuum. Based on the definition, conduction is the process that moves energy from one object to another when they are touching physically. Vacuum is a space that has nothing in it. Both conduction and convection can’t happen in vacuum. Vacuum separates the inner chamber with the surrounding environment so the inner part of the vacuum flask can contact nothing outside physically. It greatly minimizes the conduction and achieves the goal of heat preservation. Also, the screw-on stopper is usually made of plastic because plastic is one kind of insulators that have bad ability of conduction. The choice of plastic helps the poor conduction between the fluids in the bottle with the stopper, which eliminates the loss of heat effectively.
Secondly, both the vacuum and good gas tightness of the vacuum flask prevent the convection which is the process that transfers energy by the movement of large numbers of particles in the same direction within a liquid or gas. Since the convection can’t happen in vacuum, the bottle mouth is the place convection can happen. The design of the screw-on stopper avoids the outer air to come in as well as the inner air goes out. So convection cannot happen in gas, which helps the preservation of heat in the bottle. The convection of liquid inside the bottle can only make the temperature of the liquid same and even.
Finally, radiation is also blocked by the silvered surface of the glass layers. Radiation is the energy that travels by electromagnetic waves. People usually can’t see the electromagnetic waves through eyes. Also, the vacuum can’t block it. So the designer uses a new strategy to prevent radiation that is to make a silvered surface for the two layers of glasses because silver can prevent the passing of electromagnetic waves. When the radiation of the liquid radiates out in all directions, the silvered surface of inner chamber will reflect the radiation back into the liquid again. So the heat will not escape, which avoids the loss of heat.