A cover for a cushioning element, such as a pillow, volume adjustable. The cover includes one or more gathering elements that can alter a length and a volume of the cover. Each gathering element may extend around an end of the cover (e.g., circumferentially, helically around a circumference of the cover, etc.). Each gathering element may enable adjustment of the length and volume of the cover in extremely small increments or even continuously (i.e., in micro adjustments). The length and volume of the cover may be adjusted in a manner that limits or prevents migration of a cushioning element (e.g., an infill material, etc.) within the cover. A cushion, such as a pillow, may include a volume-adjustable cover with a cushioning element therein. Methods for adjusting the manner in which a cushioning element supports, molds around, underfills, and/or backfills a load and its form are also disclosed.