A pillow relies on a shell containing two types of fill material, one comparatively smaller, granular, and characterized by a comparatively larger spring constant, and another comparatively larger, more chunky in shape, and characterized by a comparatively smaller spring constant. Below a threshold level of force (or pressure, which is force per unit area) the larger, softer, second fill material resists flow of the smaller, harder, stiffer fill material. However, upon application of a force (or pressure) above some threshold, the mixture of the two fill materials will flow to conform the pillow to the shape of a user. The pillow will then substantially stabilize in that shape in the absence of forces above the threshold level.
