Mattress Foundation:

From Wikipedia, the free encyclopedia
There are three main types of foundations.

* Box-springs consist of a rigid frame that contains extra-heavy-duty springs. This type of foundation contributes to softer support and a bouncier mattress. Because box-springs can cause mattresses to sag, many manufacturers add high-density block foam underneath the coils or provide a rigid foundation instead.
* Traditional wood foundations are usually made of soft woods, such as pine, or hard woods. They usually consist of seven or eight support slats covered with paperboard or beaverboard. This type of foundation, called a zero deflection unit or an “Ortho Box” in the bed industry, increases the feeling of firmness and stability.
* Grid foundations are a combination of steel and wood.