A coil-in-coil spring is provided that exhibits a variable and non-linear loading response. The spring includes a first spring portion having a first spring constant, a second spring portion having asecond spring constant less than the first spring constant, and a third spring portion having a third spring constant less than the first spring constant and less than the second spring constant. Thefirst spring portion forms an outer coil of the coil-in-coil spring and the second spring portion, the third spring portion, or both the second spring portion and the third spring portion are positioned within the first spring portion and form an inner coil of the coil-in-coil spring. A multi-coil spring is also provided that includes an outer coil, an intermediate coil positioned within the outercoil, and an inner coil positioned with the intermediate coil.