Mattresses need a foundation in order to provide support for the person sleeping on the bed. One thing a person doesn't need is two foundations. Therefore if your bed has slats don't buy a box spring because it's not needed. When shopping for a bed frame pay special attention to the base and whether or not it comes installed with slats. For those that prefer box springs, a slatted bed base will not suit you.
What are Slats?
Slats provide support in the form of wooden or metal supports that run across the width of the bed. Some bed bases have slats already built into the frame while other bed frames are open and can support either slats or a box spring, but not both. The number of slats that are required to run across the width of your bed can depend on several factors, but on average they are spaced no more than three inches apart.
Box Spring or Slats
For those undecided if they would prefer a box spring or slats, purchase a standard bed frame that will allow for the choice of slats or a box spring. A box spring will raise the height of the mattress significantly over the height you get with slats. You can purchase both box springs and slats separately, but slats, depending on the materials used for construction, will cost less money than a standard box spring. The slats and box spring when used on an open bed frame, will rest on the outer edges of the frame.
Some furniture such as daybeds, futons or bunk beds may come with a slat foundation built into the design. In these cases don't use a box spring because it will not add extra support or comfort to the sleeper. Instead it will add extra stress and pressure to the foundation. Some slat foundation designs include a hybrid of metal and wood with a metal frame and wooden slats. Other slat foundations are composed entirely of metal or entirely of wood.
Slats provide a unique advantage over box springs outside of the need for an extra piece of bulky furniture. Slats can be changed independently of one another. If a slat cracks, it's possible to replace one slat and not have to purchase an entire foundation. A box spring on the other hand will require a replacement or more in-depth repair should it crack. Slats are better suited for foam or latex mattresses due to their ability to conform to the slats and provide increased support.