Eiderdown is the soft under layers of feathers harvested from the eider duck. The material has been prized historically for use as a warming insulating layer in clothing and bedding, especially in Northern regions, where cold weather necessitates excellent insulators. Although it has largely been replaced with down from other birds, such as geese or artificial products like Primaloft®, there is still a market for it, and high end bedding especially tends to be made with this material. Iceland is one of the world's major producers.
Down is a soft insulating layer of feathers that can be found underneath the larger body feathers of aquatic birds. The external feathers keep water from coming into contact with the skin of waterbirds, while down creates an airy layer of insulation that keeps the body of the bird warm. Eiderdown has remarkable insulating properties, being highly efficient and extremely lightweight. It is also very soft to the touch, without the scratchy quills that are sometimes found in goose down.
The eider duck is native to the Northern hemisphere and can be found in many Northern nations. The male of the species is black and white, while the female is colored in shades of brown. Both ducks are very stocky, and have wedge-like bills that are quite distinctive. When the ducks settle down to nest, they pull out their insulating down to line the nest. After abandoning the nest, the feathers are available for harvest.
Not only is eiderdown harvesting not harmful to the birds, it actually helps them. In nations that harvest significant amounts of this material, there are large regions set aside for the ducks to nest in. These protected areas also shelter other wetland species. Eider ducks are not hunted or harassed, and they tend to be rather outgoing and friendly as a result. The painstaking harvest process does make this type of down more expensive than other comparable products, however.
Comforters are classically made with eiderdown, since a large one can get quite heavy when made with other materials. It is also used to make extremely soft pillows and feather beds. Some people may be allergic to down, so they'll need to use a tight, hypo-allergenic wrap and cover for these products, if they wish to use them. Other consumers should also look out for holes that may leak the down, since the lightweight, fluffy material can quickly end up everywhere if it is allowed to escape.