Why a pillow is less density than a block of lead sinker?

A pillow is less dense than a block of lead because lead is a much heavier and compact material, resulting in a higher density. The density of an object is determined by its mass divided by its volume, so the more mass packed into a given volume, the higher the density. Pillows are typically filled with light, fluffy materials like feathers or polyester fibers, which have a lower mass per unit volume compared to lead.