Abstract: A spring is provided that exhibits a variable and non-linear loading response upon compression. The spring comprises a continuous wire having a lower end convolution, an upper end convolution, and a plurality of helical intermediate convolutions. The upper end convolution, the lower end convolution, and the helical intermediate convolutions each have a respective diameter, with the continuous wire further defining a pitch between the various convolutions. In the spring, one or more of the diameters of the convolutions or one or more of the pitches varies along the length of the continuous wire such that the spring exhibits a non-linear loading response upon compression. A mattress is further provided and includes a plurality of the springs arranged in a matrix.