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A white glazed ceramic mug branded with the Wikipedia logo

A mug is a sturdily built type of cup often used for drinking hot beverages, such as coffee, tea, or hot chocolate yet it can also be used for cold beverages. Mugs, by definition, have handles and often hold a larger amount of fluid than other types of cups.

In more formal settings, a mug is usually not used for serving hot beverages; a tea cup (or coffee cup) is preferred for tea or coffee. Many mugs are made of ceramic materials such as earthenware, bone china, porcelain, or stoneware. Types of glass, such as Pyrex, can also be used, with plastic, steel, or enamelled metal being popular for campers. Mugs can be printed with a silkscreen print, or for more complicated logos, the logo is applied onto a decal and then fired onto the mug.

A travel mug is a variation on the traditional mug that is better for transporting hot liquids. It may or may not be a vacuum flask, but is usually well insulated and completely enclosed, with an easily closed opening on the top for drinking and a handle on the side.

A puzzle mug is a novelty mug that is counter-intuitive to drink from. It will usually have several holes in it, making it impossible to drink from in the normal way. The solution to drinking from a puzzle mug is often to cover up all the holes or to discover a hidden method of drinking, such as drinking through a hollow handle.

Though at first glance a very simple object, the mug serves a number of functions which make it especially suited to holding hot, brewed liquids.

The simplest function is provided by the handle, which provides a cool area of the mug, insulated from the hot liquid by distance and ideal for grasping.

The second function is necessitated by the fact that hot beverages may be at temperatures of 80-95 degrees Celsius, which is too hot to be drunk. The thick walls of a typical mug will absorb much of this heat when the liquid is first poured into the mug, bringing the temperature of the beverage down closer to potable levels.

The third function of the mug is to trap, and hence store, heat from the beverage.This prevents the beverage cooling too quickly. The design of a mug helps insulation:first, the thick walls of the mug separate the beverage from the cool external air. Secondly, an indented base separates the beverage from the surface upon which the mug is set. The form of the base is what produces the characteristic O-shaped stain, so often seen upon desks and documents.