A breadbox or a bread bin (chiefly British) is a container for storing bread

Bread

Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...

 and other baked goods to keep them fresh. They were a more common household kitchen item until bread started being made commercially with food preservative

Preservative

A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....

s and wrapped in plastic. Breadboxes are still used by many people to store commercially purchased bread, but are used more especially by people who bake bread at home. Newer ones are usually made of metal. In the past they were often made of wood or sometimes pottery (pottery breadboxes are also called bread crocks). Old breadboxes can be collectible antiques

Antiques

An antique is an old collectible item. It is collected or desirable because of its age , beauty, rarity, condition, utility, personal emotional connection, and/or other unique features...

.

Working theory

Bread does not go stale

Staling

Staling, or "going stale", is a chemical and physical process in bread and other foods that reduces their palatability. Stale bread is dry and leathery.-Mechanism and effects:...

 by "drying out" - stale "dry" bread weighs the same as moist "fresh" bread, indicating almost no loss of water. Bread goes stale

Staling

Staling, or "going stale", is a chemical and physical process in bread and other foods that reduces their palatability. Stale bread is dry and leathery.-Mechanism and effects:...

 through a process of retrogradation

Retrogradation (starch)

Retrogradation is a reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, causing the liquid to gel....

, in which the starch transposes to a crystalline form in the presence of the water contained within the bread itself. The process speeds up at cooler temperatures, such as under Refrigeration

Refrigeration

Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

, and thus bread stored at room temperature remains fresher for longer periods than refrigerated bread. (Frozen bread, however, traps the moisture as ice, and prevents the staling process.)

Breadboxes are thus designed to:

• Keep their contents at room temperature, prolonging edible storage time.
• Have a lid loose enough to allow airflow, reducing condensation
  Condensation
  Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
  
  , which helps to prevent the formation of mould
• Have a lid tight enough to protect their contents from mice and other pests.

As a saying

The most common reference to breadboxes is the phrase "Is it bigger than a breadbox?" when trying to guess what some surprise object may be. This question was popularized by Steve Allen

Steve Allen (comedian)

Stephen Valentine Patrick William "Steve" Allen was an American television personality, musician, composer, actor, comedian, and writer. Though he got his start in radio, Allen is best known for his television career. He first gained national attention as a guest host on Arthur Godfrey's Talent...

 on the American game show What's My Line?

What's My Line?

What's My Line? is a panel game show which originally ran in the United States on the CBS Television Network from 1950 to 1967, with several international versions and subsequent U.S. revivals. The game tasked celebrity panelists with questioning contestants in order to determine their occupations....

and remains a popular question in the parlor game 20 Questions. Breadboxes are most commonly big enough to fit one or two average size loaves of bread — about 12 inches wide by 6 inches high and deep (30 cm x 15 cm x 15 cm).