Open box We like to think of a box spring as the backbone for your mattress. The best kind should be flat, level and built to keep your mattress in tiptop shape; and that’s just what the Smart Box Spring does! With its easily assembled, dependable steel structure, you can rest assured that your mattress will be sitting pretty. An included poly jacquard cover blends with the rest of your bedroom, and with a variety of different thicknesses to choose from, you can pick the one you need to customize the height of the bed