Spa Sensations 7.5″ Bi-Fold Box Spring, Multiple Sizes The Spa Sensations Bi-Fold Box spring is the perfect foundation solution. Simply remove the box spring from the shipping carton, unfold, lay your mattress on top and have a great nights sleep. This box spring features the look of a traditional box spring and heavy gauge steel for long lasting durability. It is easy to move into tight spaces and saves on costly freight charges as it comes folded in a box.