Insulating container in real life Is it possible to practically build a perfectly insulating container? If not, what's the best way to build one? By perfectly I mean no heat is trasferred over an infinite amount of time.
 A: As Harish Chandra Rajpoot removed his answer instead of rectifying to:
"No, it is not possible to practically build a perfectly insulating container, but even in commercial products we try to get as close as we can get, for example, a "thermos""
The problem is that no material exists that reflects 100% of all electromagnetic radiation, and so, you cannot contain radiation energy dissipation from a closed system within our universe. In other words, every material radiates energy (black body radiation), and it is not possible to contain all this radiation inside one single container. But then we can try our best and use materials that reflect as much as possible back into the thing we want to isolate.
Addressing now the other forms of energy dissipation: convection and conduction. Convection, for liquids and gases, is easy to handle, just build a vacuum around the thing you want to isolate. But then you have conduction. Either you suspend your thing in vacuum, using for example some form of electro-magnetic levitation or you have the container passively supported via physical solid contacts. In the first case, you are wasting energy just to be sure your container stays in no contact with your outer vacuum walls, in the second, contact means there is conduction of heat between your container and the outward vacuum walls, also dissipating heat.
So, in short, we cannot. But the closest we can get, we try, i.e. in refrigerators or thermal-bottles.
A: It's not practically possible to build a perfectly insulating container as there is no perfect insulating material. But a closed container can be very close to a perfectly insulating container.
Vacuum offers the highest thermal resistance to the conduction and convection heat transfers. Therefore vacuum is the best insulator for preventing conduction and convection heat transfers.
Similarly, a highly polished or shiny surface like silver or aluminium foils\shields can be used to prevent the radiation heat transfer. If we use a large number of thin radiation shields, the heat transfer becomes almost negligible.
If we place a large number of thin (foil) radiation shields keeping a vacuum gap between each two shields in form of spherical shells, a spherical closed container (a cork less) can be practically made  such that the heat transfer through it becomes almost negligible ideally zero over very long period of time.

