There are many ways this is done. It can be done by having a double walled thermos with either air, an insulator, or a vacuum between. A vacuum will prevent all conduction except where the two walls touch but requires stronger materials.
There is air between the inside and outside of the flask.
The vacuum reduce heat loss by conduction and convection.
Using vacuum as an insulator avoids heat loss by conduction. Heat transfer is minimised by reflective silver surfaces that are applied to the flask. This prevents thermal radiation from entering and escaping the flask.
A glass thermos 'bottle' is constructed as a bottle-within-a-bottle and there is a slight vacuum between the bottles, since heat can't travel within a vacuum it will keep the contents hot/cold for a long time. In addition, they usually have a mirror coating on the outside to reflect hot/cold from the environment. The cap usually is hollow with an insulating material like cork or poly-foam.
The vacuum flask otherwise known as a thermos flask
There is air between the inside and outside of the flask.
The vacuum reduce heat loss by conduction and convection.
This reduces heat transport through conduction and convection.
Using vacuum as an insulator avoids heat loss by conduction. Heat transfer is minimised by reflective silver surfaces that are applied to the flask. This prevents thermal radiation from entering and escaping the flask.
Thermos flask is a thermos container used to store liquids like any hot drink. The liquid added to thermos flask will retain the temperature even after some time irrespective of external temperatures.
out of steel
inside a thermos is flask steel materials, it keeps the thermos for about 1 - 2 days.
There is a dead air space between the liner of the thermos and the outside. This space acts as insulation preventing conduction. In a really good thermos, or Dewar flask, the space is actually a vacuum. Vacuum is an even better insulator than air is, since heat doesn't conduct across a vacuum at all.
A Thermos.
A glass thermos 'bottle' is constructed as a bottle-within-a-bottle and there is a slight vacuum between the bottles, since heat can't travel within a vacuum it will keep the contents hot/cold for a long time. In addition, they usually have a mirror coating on the outside to reflect hot/cold from the environment. The cap usually is hollow with an insulating material like cork or poly-foam.
Thermos flask or vacuum flask.
Hot drinks are usually put in a thermos flask, so the flask needs to be made of something strong in order not to get ruined in any way, therefor steel is used.