Coil-in-coil spring with variable loading response and mattresses including the same

A coil-in-coil spring, comprising a continuous wire forming an inner coil having a substantially conical shape and an outer coil extending around the inner coil and having a substantially cylindrical shape;

• wherein the inner coil includes a plurality of helical convolutions and an upper end convolution, the plurality of helical convolutions of the inner coil extending from a lower end of the coil-in-coil spring to the upper end convolution of the inner coil, said inner coil increasing in diameter and pitch from said upper end convolution to said lower end;
• and,
• wherein the outer coil includes a plurality of helical convolutions and an upper end convolution, the plurality of helical convolutions of the outer coil having said cylindrical shape and extending from the lower end of the coil-in-coil spring to the upper end convolution of the outer coil, said outer coil having a constant diameter and constant pitch;
• wherein said outer coil has a first spring constant, said inner coil has a second spring constant, said second spring constant being different than said first spring constant;
• wherein the varying diameter and pitch of said inner coil provides the coil-in-coil spring a variable and non-linear response to loading;
• wherein an uncompressed height of the inner coil is about 75% of an uncompressed height of the outer coil.