The facing surfaces of glass bottles are coated with a silver solution. They act like mirrors and reflect much of the heat coming from inside or outside the container. In doing so, they prevent heat transfer by radiation. In stainless steel vacuum bottles, a layer of copper foil between the inner and outer bottles serves the same purpose. Other features of vacuum bottles help minimize both the loss or entry of heat.
Most vacuum bottles have a small mouth, which reduces heat exchange.
The bottles are closed with a stopper made of cork, plastic, or some other material that conducts heat poorly. The inner container of a vacuum bottle is encased in metal or plastic. A rubber collar around the mouth holds the inner container in place, and a rubber cushion at the base serves as a shock absorber.