A foundation is a solid structure that provides support between the mattress and the bed frame, while a platform bed acts alone without the need for a separate foundation and frame. Generally made out of wood, a foundation is meant to take the place of a box spring and offer greater support, allowing them to accommodate heavy mattresses. A foundation can help preserve the life of the mattress, but it may increase its firmness. Platform beds include a built-in support system designed to replace a box spring. This may include a slatted, lattice, metal grid, or solid platform.