Let’s unpack what a box spring actually is, why you may or may not need one, and where it could set you and your mattress up for success. Engraving depicting a coiled spring mattress, demonstrating its lightness compared with a feather or a feather and spring mattress of a similar size. This is a deliberate design choice, because the coils in the box spring are springing up to meet the mattress atop it. But why does this coil type need a box spring in the first place? Ultimately, it came down to making sure sleepers were truly getting support across the board, er, box spring.