Though at first glance a very simple object, the mug serves a number of functions which make it especially suited to holding hot liquids:
The mug stores some heat from the beverage, and so prevents it from cooling too quickly. The design of a mug helps insulation: (i) thick walls separate the beverage from the cool external air, and (ii) an indented base separates the beverage from the surface upon which the mug is set. The shape of the base forms the characteristic O-shaped stain, so often seen upon desks and documents.
