Box springs are the mattress foundation that sits under most mattresses and functions both to absorb shock from nighttime movement and to elevate the mattress to a sitting position. Adjustable box fits all King, Queen, Twin or Full sized mattresses (up to 14″ thick). A must to keep your mattress or box spring clean during a move, shipping or when placing the mattress in storage. Buy Zinus Compack Adjustable Steel Bed Frame, for Box Spring & Mattress Set, Fits Full to King: Bed Frames – Amazon.com FREE DELIVERY possible on eligible purchases Why you’ll love it: Helix offers excellent customization options straight from its website, so you can get the mattress that’s perfect for you. Mattress startup Helix ships its beds in a box, too .