Female wildfowl use down feathers plucked from their own breasts to line their scrape nests. This process performs the dual function of helping to insulate the eggs and exposing the female's brood pouch—an area of bare skin, rich in blood vessels, which transmits heat very efficiently. Of the various items birds use to line their nests, down feathers provide the most effective insulation, though only when dry; wet down is the least effective insulator. Down may also help camouflage the eggs when the female is away from the nest, particularly as the birds often draw the feathers over their eggs before leaving.