Sleep the Way Nature Intended. Drift into restful sleep each night-naturally. With the King Koil Natural Retreat Box Spring Foundation, you'll experience unparalleled temperature regulation, pressure relief, reduced motion transfer, and ultimate comfort. This box spring foundation extends the lifespan of your mattress. A foundation provides a solid, even surface for your mattress, preventing sagging and uneven wear. This support helps maintain your mattress' shape and comfort for years longer than using it directly on the floor or an unsupportive base.