Fill Power

Fill Power is a measurement of down insulation quality that indicates how much space one ounce of down occupies in cubic inches when fully lofted. Higher fill power numbers (typically ranging from 400-900+) indicate better quality down that traps more air and provides superior warmth-to-weight ratios in sleeping bags, jackets, and other insulated outdoor gear. This metric helps campers and backpackers compare the thermal efficiency and compressibility of down products, with higher fill power generally meaning warmer, lighter, and more packable gear that's ideal for backcountry adventures where weight and space are critical.