Like all support layers, innersprings control how deeply your body is permitted to sink into the mattress. This is one of the most affordable support cores, so there is no surprise that it is also the most popular. Innerspring mattresses vary in coil count and gauge size, but they basically fall under one of the four categories: bonnell, continuous, offset, and pocket. So, although most mattresses pretty much look the same from the outside, they are all very unique inside. With Innerspring support cores, wire coils comprise the support structure of innerspring mattresses. A heavy duty border wire provides support to the coils to help reduce sagging, so it can better retain its shape.