It's very easy to be confused about these three mattress terms — especially since the industry routinely misuses the terms. A true box spring is made of wood and "springs" or coils in a steel grid pattern. The springs inside the box spring provide "give" to the innerspring mattress on top. (Box springs are only used with innerspring mattresses.) The mattress industry moved away from using traditional box springs almost 20 years ago, replacing them with foundations.
However, the term "box spring" is still frequently used because so many people are accustomed to it. Today, most manufacturers make foundations. A foundation is a sturdy flat structure that is usually constructed of wood, with a flat corrugated board on top. Some foundations may include metal in the construction.
Foundations offer superior support for a wide variety of mattresses, including memory foam, latex, innerspring, and airbed mattresses because the solid surface helps to prevent premature sagging of the mattress. A platform bed is a piece of furniture that doesn't require a foundation or box spring. With this type of bed, you put your mattress directly on the platform. Platform beds are typically made of wood, and contain a series of wooden slats that run across the bed.
A flat piece of wood can be used instead of slats to offer a solid surface for better support. (Platforms that use slats instead of a built-in foundation — or board — may require a Micro Foundation if the slats are more than a couple inches apart for proper support.) Whether you use a box spring, foundation or platform bed, it's important that it has a center support if you have a queen- or king-sized mattress, as most manufacturers require this to prevent voiding the warranty.