Bed base

A bed base, sometimes called a foundation, is the part of a bed that supports the mattress. The bed base is itself held in place and framed by the bedstead (bed frame). In the United States, box-spring bed bases are very common (to the point where 'bed base' and 'box spring' may be used synonymously). In Europe, sprung slats are much more common.

A bed base

There are three main types:

• A traditional box spring consists of a rigid frame containing extra heavy duty springs. This foundation is often paired with an innerspring mattress, as it extends the life of the spring unit at the mattress's core.
• An all-wood foundation usually has seven or eight support slats disposed below paperboard or beaverboard. This foundation, variously called a "no-flex", "low-flex" or zero-deflection unit, as well as an "ortho box", provides support similar to a platform foundation. All-wood foundations have become increasingly prevalent as U.S. mattress makers shifted to super-thick, one-sided mattresses.[1]
• A grid-top foundation is a combination of steel and wood.

Typically the measurements of a foundation will be about 1-2" shorter than the measurement of a mattress.