Abstract: A spring core for a mattress consisting of a plurality of side-by-side rows of identically configured helical coil springs each made of a single piece of wire having a central portion of a first radius defining a central spring axis and terminating at opposing ends with unknotted upper and lower end turns disposed in planes substantially perpendicular to the spring axis. The springs are connected with each other at their upper and lower turns by connecting lacing wires. The upper and lower turns are each substantially U-shaped, having a longer relatively straight leg and a shorter arcuate leg located at the free end of each end turn, the legs connected to each other by a base web. The radius of the shorter arcuate leg is substantially less than the first radius of the central portion of each coil spring. All the coil springs are oriented in the same direction, except along an edge region of the spring core.