Thermos bottle or Dewer flask consists of a double walled glass vessel with inner and outer walls coated with silver. Give reason.

Explanation

A dewar flask or thermos bottle is a device to minimize heat transfer between the contents of the bottle and outside. It consists of a double walled glass vessel with inner and outer walls coated with silver. Radiation from the inner walls is reflected back into the contents of the bottle. The outer wall similarly reflects back any incoming radiation. The space betsween the walls is evacuated to reduce conduction and convection and the flask is supported on an insulator. The device is useful for preventing hot contents like tea from getting cold.